This photo from Reuters reportedly shows an explosives-filled vehicle exploding east of Mosul, during clashes between IS militants and Kurdish Peshmerga fighters.

Image source, Reuters

IS has claimed a number of suicide attacks targeting pro-government forces outside Mosul - but has not made any official comment on the launch of the offensive.

The IS-linked news agency, Amaq, reported that eight suicide attacks had targeted Iraqi and Kurdish Peshmerga forces "trying to advance" from the east of Mosul. 

Amaq also said all efforts to take IS-held villages in that region had thus far failed - contradicting reports from security sources.

An Iraqi security source tells Beirut-based Iraqi al-Sumaria TV that the mobile phone service in Mosul has been restored, after IS had cut it off. 

The source, in Nineveh province, says the Iraqi authorities have also set up "toll-free numbers for citizens to provide information to the security forces" on IS positions.

BBC Monitoring reports that State-sponsored al-Iraqiya TV is quoting the Popular Mobilisation, a Shia-led paramilitary force, as saying the IS security chief in southern Mosul, Ahmed Khattab Omar, has been killed.

Up to 100,000 Iraqi civilians may flee to Syria and Turkey to escape the military assault in Mosul, the UN says. 

The UN High Commissioner for Refugees has issued an appeal, external for an additional $61m (£50m) to provide tents, camps, and winter items such as blankets for displaced people inside Iraq and the two neighbouring countries. 

The charity Save the Children says more than half a million children are endangered by the Mosul offensive.

It is calling for safe routes to be established for those fleeing the city.

These women, with their small children, were photographed by Save the Children at a checkpoint near the city of Kirkuk, about 140km (85 miles) south-east of Mosul.

The charity said they had fled on foot on a two-day journey from the nearby IS-held town of Hawija through deserts and minefields.

Image source, Save the Children / Ruairidh Villar

Our correspondent Orla Guerin is with Kurdish Peshmerga forces to the east of Mosul and gave us a sense of what has been happening on the ground in the past few hours.

Witnesses in Mosul meanwhile tell the BBC that residents are going about their business as usual, with shops in the city centre still open.

IS militants had left the centre to engage in battles in the outskirts, the witnesses say.

A source at the Iraqi military's Nineveh Operations Command source tells the BBC that combat units of the army's 9th Division have inflicted heavy losses on IS forces in the Hamdaniya district, east of Mosul.

The BBC's Turkey correspondent, Mark Lowen, explains: 

"Turkey has always seen Mosul as its 'sphere of influence': a city with an ethnic Turkmen and Sunni majority in which Sunni Turkey holds sway. 

"And President Erdogan is desperate not to let that power slip.

"In his speech, he stressed Turkey's role in training Iraqi Sunni fighters and Iraqi Kurdish Peshmerga. 

"But that is exactly what has caused frictions with the Iraqi government in Baghdad, which says that Ankara did not get its permission to have troops stationed there. 

"The US has to tread a fine line: it needs Turkish support in the anti-IS coalition but knows the Iraqi army must play the lead role in the offensive. Pleasing both sides in this escalating row will be a tough task."

Turkey's President Recept Tayyip Erdogan says his country "cannot be excluded" from the Mosul operation. 

In a televised speech, he vowed that Turkey "will be at the table".

About 1,500 Turkish-trained Iraqi fighters are participating in the operation, but a political row between Baghdad and Ankara has put Turkey's role in doubt.

The advance of Kurdish Peshmerga forces east of Mosul began "more quickly than we expected" on Monday morning, the BBC's Orla Guerin says.

But it has slowed in places as they encounter resistance - giving troops a chance to rest.

Kurdish news network Kurdistan24 has broadcast footage of what it describes a US-led coalition air strike on an IS position east of Mosul.

Iraqi security sources tell the BBC that Kurdish Peshmerga fighters are advancing on Qaraqosh and Bartila, in the Hamdaniya district east of Mosul. 

They have so far managed to regain control of five nearby villages - Kabirli, Basakhrah, Badanah Uliya, Badanah Sufla and Shaqouli.

US-led coalition warplanes have been carrying out air strikes across Hamdaniya in support of the operation, according to the source.

Image source, Reuters

The UN and its humanitarian partners have set up camps for the 200,000 civilians who are expected to flee Mosul and its surrounding area in the first weeks of the offensive.

In preparation, they have stockpiled about 50,000 emergency shelter kits containing timber, tools, and tarpaulins. Another 30,000 kits are expected to be delivered in the coming weeks.

However, UN officials have warned that as many as 1.5 million people could end up being affected by the Mosul offensive.  

The Kurdish Rudaw news agency has posted a video it says shows an attempted IS suicide vehicle bomb attack on Peshmerga fighters east of Mosul. 

The footage appears to show a speeding vehicle approaching the front line and coming under fire. The view is obscured when the cameraman takes shelter, before an explosion is heard.

Rudaw says there were no Kurdish casualties.

It is feared the battle for Mosul could see up to 1 million Iraqis flee their homes, and that those who remain could be caught in the crossfire or used as human shields.

A UN refugee agency (UNHCR) representative for Iraq told the BBC last week that IS militants "know where the routes out of the city are and they will kill people escaping".

Emergency camps have already been set up in areas around Mosul - with more planned to cope with the mass exodus.

Read more: UN prepares for aftermath 'chaos'

As Kurdish forces advance from the east of Mosul, Iraqi soldiers are moving northwards from Qayyarah airbase, about 60km (37 miles) from Mosul.

The airbase, which was recaptured in July, is being used as a logistics hub for the offensive. 

The facility has been refurbished to enable the landing of cargo aircraft, enabling ammunition, fuel and rations to be flown directly to the frontline rather than being trucked up from depots near the capital, Baghdad. 

Hundreds of US military advisers are also at Qayyarah to advise and assist the offensive. 

The Kurdish news agency Rudaw posts video is says shows oil wells on fire in the Hamdaniya area, east of Mosul.

IS has used the strategy before to impede air support from US-led coalition warplanes, notably around the town of Qayyarah in August.

Our correspondent, Orla Guerin, said the mood among the Peshmerga was "very upbeat".

"Many of them seemed eager for this long-awaited offensive to begin - people were going by us on top of their military vehicles doing high-fives," she added.

Some were posing for selfies on their way to the frontline.

One Kurdish general said: "If I am killed today in battle, as I well may be, I will die a happy man because I have done something from my country."