Throughout the day, both #FranzFerdinand and #WWIII have been trending on Twitter.

In June 1914, Austrian Archduke Franz Ferdinand was shot dead - along with his wife - in Sarajevo, Bosnia.

Following the shooting, countries scrambled to take sides and it started off a chain of events that led to World War One.

Parallels are now being drawn to the killing of Gen Qasem Soleimani in Iraq.

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Image source, Getty Images

If you're just joining us, here's what been happening:

• Overnight, the US killed Iran's most powerful military commander Qasem Soleimani and other Iran-backed militia figures in a targeted air strike, representing a dramatic escalation of tensions
• The US said it had carried out a drone strike at the direction of President Donald Trump "to protect US personnel abroad" from a man they had long considered a threat
• The surprise move came after ratcheting US-Iran tensions. Last week, Iranian-backed militias killed a US contractor in Iraq prompting US strikes on the Kataib Hezbollah militia in western Iraq and eastern Syria. Violence then erupted outside the US embassy in Baghdad, which President Trump blamed on Iran.

• Soleimani was the leader of the elite Quds Force. He was close to Iran's Supreme Leader Ayatollah Ali Khamenei, and was widely seen as the second-most powerful man in Iran

• Iran immediately condemned the attack, and later vowed to exact "harsh vengeance". Protesters in the country have taken to the streets, destroying US and Israeli flags
• President Trump, however, tweeted , externalthat Gen Soleimani was "both hated and feared within the country", adding: "He should have been taken out many years ago!"
• Funerals for Gen Soleimani and Iraqi Shia militia leader Abu Mahdi al-Muhandis, who was killed in the same strike, are being held on Saturday morning
• Amid the escalating tensions, politicians from other countries appealed for calm as oil prices initially jumped

Newly released footage shows more than 650 US troops arriving in Kuwait just hours before the air strike on Baghdad International Airport that killed Gen Qasem Soleimani.

Earlier this week, US Defence Secretary Mark Esper announced that more troops would be deployed to the region following an attack on the US embassy in Baghdad. There are about 5,000 US troops already stationed in Iraq.

Both President Donald Trump and Secretary of State Mike Pompeo have said the air strike in Baghdad was carried out in response to an "imminent threat" from Gen Soleimani and the Quds forces he led.

Bahrain-based airline Gulf Air has suspended all flights to the Iraqi cities of Baghdad and Najaf until further notice.

The company tweeted that this was due to "safety and security issues".

The funerals of Gen Qasem Soleimani and Iraqi Shia militia leader Abu Mahdi al-Muhandis will be held on 4 January.

Iraq's Shia paramilitary Popular Mobilisation Forces (PMF) announced on Facebook that the funerals would take place in Baghdad at 10:00 (07:00 GMT).

"The official funeral would be followed by a popular one from the gate of the Green Zone [which houses the US embassy] at 11:00 (08:00 GMT)," the militia added, urging all Iraqis to take part.

Jeremy Bowen
BBC Middle East Editor

Iran has sworn vengeance. That threat has to be taken seriously. Soleimani was at the core of the regime, and a talisman for Iran's hardliners. They will want to get even, perhaps more than that.

Despite arms embargoes, Iran has developed a modern arsenal of rockets and missiles. But if it wanted to use them against US forces as part of a reprisal, Iran would risk making matters worse.

An act of war to answer that of the US - for example attacking US ships in the Gulf, would risk provoking a devastating response. Iran's oil refineries are on the coast and would be easy targets for the vast firepower the US has in and around the Gulf.

When Iran retaliates it is likely to follow Soleimani's own indirect tactics, so-called asymmetric warfare, spurning an attack through the front door for one through a side window.

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His death is at the centre of today's news - but who was Qasem Soleimani?

Here, BBC Middle East Correspondent Quentin Sommerville talks about the "electrifying figure" at the top of Iran's military.

Senate leader Mitch McConnell and minority leader Chuck Schumer are expected to speak on the Senate floor at about midday local time (17:00 GMT) and comment on the killing of Gen Qasem Soleimani.

Earlier, CNN reported that Senator Schumer had not been given advance notice of the air strike in Baghdad.

Image source, Reuters

So far, President Donald Trump has only commented on social media - tweeting that "Iran never won a war, but never lost a negotiation".

He later elaborated: "General Qasem Soleimani has killed or badly wounded thousands of Americans over an extended period of time, and was plotting to kill many more... but got caught!"

Mr Trump then tweeted again, after the strike was criticised by Iraq's parliamentary speaker.

Iran's National Security Council has vowed to exact "harsh vengeance" on the US for the killing of Gen Qasem Soleimani.

"The US regime will be responsible for the consequences of this criminal adventurism," the council said in a statement to Iranian media.

"This was the biggest US strategic blunder in the West Asia region, and America will not easily escape its consequences."

It did not elaborate on any action Iran is considering - only that it had taken "appropriate decisions".

It also said the killing of Iraqi Shia commander Abu Mahdi al-Muhandis in the same air strike was a "symbol of the unbreakable bond between the two nations of Iran and Iraq in the future".

Thousands of people in Gen Qasem Soleimani's home province have gathered to mourn his death.

The mourners marched through the city of Kerman, capital of the province of the same name, singing and waving photos of Gen Soleimani after Friday prayers.

Image source, EPA

UN Secretary-General Antonio Guterres says he is "deeply concerned" by the US strike, and has called for world leaders to show "maximum restraint".

"The Secretary-General has consistently advocated for de-escalation in the Gulf," his spokesman Farhan Haq says.

"He is deeply concerned with the recent escalation.

"This is a moment in which leaders must exercise maximum restraint. The world cannot afford another war in the Gulf."

After condemnation from a foreign ministry spokeswoman and a statement from the defence ministry, more strong words have come out of Russia - this time, from President Vladimir Putin.

Mr Putin warned that the killing of Gen Qasem Soleimani would "seriously aggravate the situation in the region", the Kremlin quoted him as saying.

President Putin made the comments during a phone call with his French counterpart Emmanuel Macron, the Kremlin added.

Image source, AFP

Image source, AFP

Iran's Supreme Leader Ayatollah Ali Khamenei has named Brig Gen Esmail Qaani, 63, as the new commander of the elite Quds Force of the Islamic Revolutionary Guards Corps (IRGC).

The force was previously led by Gen Qasem Soleimani.

According to Tasnim news agency, Brig Gen Qaani joined the IRGC in 1980 and served in the 1980-88 war with Iraq. He joined the Quds force after the war.

He has previously spoken scathingly about the US, Israel and their regional allies.

In 2018, he called the 11 September 2001 terror attacks in the US an act of "self harm" by the US, accusing Washington of carrying them out in order to "create a mess" in the Middle East.

In that speech, Brig Gen Qaani said: "Americans spent $7,000bn in the region but they achieved nothing. America is the biggest debtor in the world now."

Leading Republican Senator Lindsey Graham was briefed about the strike when he was in President Trump's Mar-a-Lago resort in Florida recently, according to CNN's White House reporter Kaitlan Collins.

Sen Graham was reportedly spotted in Mar-a-Lago on Monday and Tuesday.

Sen Graham, chairman of the Senate Judiciary Committee, is a staunch ally of President Trump.

The Turkish Foreign Ministry has joined Russia and Iraq in condemning the US strike and warned that it will "increase insecurity and instability in the region".

"We strongly emphasise a warning once again that turning Iraq into a conflict zone will hurt peace and stability," it said in a statement published by the state-funded Anadolu news agency.

Tensions between the US and Turkey, a fellow Nato member, were already growing.

Last month, talks at the Nato summit in London almost stalled over disagreements about Turkey's recent military action in northern Syria.

Image source, Reuters

Until now US President Donald Trump had remained relatively silent on the strike - publishing only a one-line tweet, and a picture of the American flag.

He has now sent two more tweets, accusing Soleimani of being "directly and indirectly responsible for the deaths of millions of people".

"He should have been taken out years ago!" he added.

Image source, Getty Images

Part of the complexity of this story is that the killing of Iran's top military commander took place on Iraqi soil, near Baghdad.

Former adversaries, Iraq and Iran have become close allies in recent years. However, the United States also maintains a troop presence in Iraq.

Iraq's parliamentary Speaker, Mohammed al-Halbousi, condemned the lethal air strike on his country's soil, saying it was "a breach [of] Iraq's sovereignty and a violation of international agreements".

He also warned that the "repercussions of such attack would threaten the stability of Iraq and the region", and urged both sides to "keep Iraq away from regional conflicts".

Dozens of US citizens working for foreign oil companies in Iraq are leaving the country on Friday, Reuters news agency reports.

The agency quoted the Iraqi oil ministry as saying many workers based in Basra were departing after the US embassy in Baghdad urged all US citizens to leave the country as soon as possible. But the ministry said staff movement would not affect its operations.

Iraq is a major producer in the global oil market, and the increase in tensions had already caused oil prices to increase.

Further to comments from Russian Foreign Ministry spokeswoman Maria Zakharova, the country's Defence Ministry has released a strongly-worded statement condemning the strike - and praising some of Soleimani's actions.

"Short-sighted actions by the US resulting in the killing of General Qasem Soleimani are leading to a steep escalation of the military and political situation in the Middle East region and serious negative consequences for the whole system of international security," the statement says, quoted by Russian news agency Interfax.

"Under Qasem Soleimani's direct leadership, armed resistance against international terrorist groups Isis and al-Qaeda was organised in Syria and Iraq long before the US-led so-called 'international coalition' was set up.

"His personal contribution to the fight against Isis in Syria is undeniable."

The statement later added: "Gen Qasem Soleimani was a skilled military commander, who wielded deserved authority and significant influence in the Middle East region."

Image source, Reuters

US Secretary of State Mike Pompeo has told US media that the air strike in Baghdad was carried out in order to disrupt an "imminent attack", which he said would have endangered Americans in the Middle East.

Speaking to CNN and Fox News, he said they made an "intelligence-based assessment" to target Qasem Soleimani.

"He was actively plotting in the region to take actions - a big action as he described it - that would have put dozens, if not hundreds of American lives at risk," he told CNN.

"These were threats that were located in the region. Last night was the time that we needed to strike to make sure that this imminent attack... was disrupted."