While we wait for the Pentagon briefing to start, we can share a new statement from the US State Department.

The department says it has been briefed on the US soldier that was detained in North Korea.

"We are aware of reports from the Department of Defense that a US service member willfully and without authorisation crossed the Military Demarcation Line into the Democratic People’s Republic of Korea (DPRK)," a spokesperson for the State Department says.

They add that the department is in touch with the US Department of Defense to provide assistance.

"Due to privacy considerations, we have no further comment at this time."

Officials with the US Pentagon are due to give a scheduled briefing on Ukraine at 12:30 local time (17:30 BST).

Secretary of Defence Lloyd Austin and General Mark Milley will inevitably face questions about the soldier that is detained in North Korea.

We are streaming the news conference live.

You can watch by clicking the play button at the top of the page.

Jean Mackenzie
Seoul correspondent

We know the soldier crossed the concrete demarcation line that separates North and South Korea while on an organised tour of the border.

He was visiting the sensitive, but unarmed Joint Security Area at the heart of the Demilitarised Zone.

I've been on one of these tours myself, so I know the spot well. This is the area with the iconic blue huts where, in the past, the two sides have met for negotiations. It's the place where the former US President Donald Trump jokingly stepped over the line himself, while negotiating with Kim Jong Un.

Typically, soldiers from the North and South stand guard on each side, facing each other. But since the start of the Covid pandemic, the North Koreans have not been there.

Instead, they stay inside a large building set back from the border, only sometimes peering out from behind the curtains. This means when the US solider decided to step across, he may not have been able to see any North Korean soldiers.

We don't know what happened next - if he made it to the building or the North Korean guards came out to get him.

The biggest unanswered question is why a US solider would choose to cross into North Korea in this way. Was this an impulsive and reckless moment, or is he hoping to stay in North Korea. And if so, why?

A spokesperson for the US military in Korea has now confirmed reports that the man who crossed the border is a US service member.

They released this brief statement moments ago.

Travis King has been identified as the US soldier detained in North Korea, according to CBS News, the BBC's partner in the US.

But beyond his name and the fact he is a member of the US military, there are a lot of questions that have yet to be answered.

• What were his motivations? So far, we have an official who says King "wilfully" crossed the border, while a witness claims he saw the soldier running across the North Korean border laughing. However, we don't know any more than that.
• Why was he there? Private 2nd Class Travis King crossed during an orientation tour of the Joint Security Area (JSA) between North Korea and South Korea, according to several news agencies. King was reportedly being escorted out of the country for disciplinary reasons when he turned around at airport security and booked a tour.
• When will be released? All we know is that King crossed the border and is now being held by North Korea, according to a statement released a few hours ago by the UN Command. US prisoners have typically been treated brutally in North Korean prisons. In 2018, North Korea released an American college student who was imprisoned for stealing a hotel sign. He returned to the US in a coma and later died.

The soldier who crossed into North Korea is Private 2nd Class Travis King, officials have told the BBC's US partner CBS News

As we previously reported, an official told CBS the soldier was being escorted out of the country for disciplinary reasons and had gone through airport security, but managed to make his way out of the terminal before joining a border tour.

A third source, a defence official, later told CBS that the soldier had "wilfully" gone across the border. His motivation remains unclear.

Officials are waiting to confirm his identity until his next of kin have been notified that he is being held by North Korea, CNN reports

Anthony Zurcher
North America correspondent

With a war in Ukraine, strained relations with China and simmering conflicts in the Middle East, the last thing US President Joe Biden needed was another foreign policy crisis.

But he has one, with one of the most enigmatic, tempestuous dictators in the world.

During Donald Trump’s presidency, US-North Korea relations warmed somewhat after a heated start, as the American president made unprecedented overtures toward Kim Jong Un. There was little to show for his efforts besides a marginal cooling of rhetoric from Pyongyang, however.

Since assuming office, Biden has put North Korea toward the back of the US foreign policy agenda, refusing to continue Trump’s diplomatic engagements. Kim has responded with over a hundred new missile tests that suggest his nuclear-delivery technologies continue to advance – possibly putting the US mainland in range of a North Korean strike.

Now Kim has a new means of forcing the US to pay attention to him – and meet his demands for respect and accommodation on the international stage. An American detained in North Korea is sure to generate international headlines.

The possibility that the individual is a US soldier will only complicate the situation, making a negotiated release more difficult. If Biden is unable to arrange a speedy resolution, it will be cited by his political opponents as an example of the current president’s limited power on the international stage.

A more forceful reaction to the incident by Biden, however, could lead to an escalation of an already tense situation on the Korean Peninsula at a time when US military resources are already stretched thin.

Image source, Getty Images

Exactly seven decades have passed since the armistice agreement of 1953 put a halt to the Korean War.

Despite this, the US still maintains a large presence in the area.

There are reportedly 28,000 American troops stationed in South Korea - making it America's third-largest foreign military presence after Japan and Germany, according to a Reuters report from 2021.

South Korea is also home to the largest US overseas military base.

The US army there works closely with the South Korean military, part of a security alliance that was forged ever since the US entered the Korean War in 1950.

More than 70 years later, the US and South Korea have continued their partnership.

That is because the Korean War never actually ended.

The armistice brought fighting to a halt, but there has never been a treaty to end the conflict between North Korea and South Korea and its allies.

And North Korea continues to be a cause for concern for both the US and South Korea, as it frequently tests its missile capabilities and is working to develop its nuclear weapons program.

You can read more about the weapons that North Korea has tested lately here.

The US national who has been detained is a soldier, according to CBS News, the BBC's partner in the US.

The soldier was being escorted back to the US for disciplinary reasons, but after going through airport security they somehow returned and joined a tour at the border, a US official told CBS.

Two US officials speaking on condition of anonymity separately told the Reuters news agency that the detained person is a soldier.

A person has spoken to the BBC's US partner CBS News, external about what they saw when the US national crossed.

The unnamed witness, who was part of the same tour group, says the man "gave out a loud 'ha ha ha'" before he ran in between some buildings in the direction of the North Korean border.

"I thought it was a bad joke at first, but when he didn't come back, I realised it wasn't a joke, and then everybody reacted and things got crazy."

They add that there were no North Korean soldiers visible when the man crossed.

"I'm telling you this because it actually hit me quite hard," the witness says. "It was on the way back in the bus, and we got to one of the checkpoints... someone said we were 43 going in and 42 coming back."

The UN Command says the US national crossed during an orientation tour of the Joint Security Area (JSA) between North Korea and South Korea.

It's still not clear who the American is or why they crossed, but tours such as this are common.

They take place specifically in Panmunjom, which has historically been the only place along the border where troops from the two Koreas face each other.

It is where the Korean Armistice Agreement of 1953 was signed, effectively ending the Korean War.

The village is also used as a meeting point. It is where former US President Donald Trump stepped foot into North Korea as he met Kim Jong-un in 2019.

A professor in South Korea tells the AFP news agency that the area is likely where the US national crossed.

"It's the only location one could attempt such a move out of the whole JSA tour," Choi Gi-il, a professor of military studies at Sangji University, said.

Image source, Getty Images

The Demilitarised Zone (DMZ) between North and South Korea is known as one of the most dangerous places in the world.

The 150 mile (240km) long border is filled with landmines, surrounded by electric and barbed wire fencing and surveillance cameras and armed guards are supposed to be on alert 24 hours a day.

Tens of thousands of troops guard it on both sides.

In total, it is about 1.5 times the size of Seoul and almost twice the size of New York City.

The strip of land, which is 2.5 miles wide, attracts thousands of tourists each year who come to see one of the most highly militarised areas in the world.

Dozens of people try to flee North Korea every year, but defections across the dangerous DMZ are rare.

The news of the crossing and detention came from the United Nations Command, which operates the Demilitarised Zone and Joint Security Area (JSA) between North and South Korea.

In a statement posted to Twitter, external, it said:

A US national is being held by North Korea after crossing the border without authorisation, the United Nations Command says.

The individual has not been named and much is still unknown about the circumstances of the crossing. The UNC said it happened during a tour of the border area.

BBC News has reached out to the US Department of State for comment.

We'll bring you live updates here as we get them.