Erbil: Sunni militants have taken control of the northern Iraqi city of Tal Afar, raising fears in the predominately ethnic Turkmen town that the extremist group will target its residents, half of whom are Shiite Muslims.

Situated about 50 kilometres from Mosul, Iraq’s second largest city and the first to be seized by the Islamic State of Iraq and the Levant (ISIL) a week ago, Tal Afar was taken by the insurgents after heavy fighting in the area on Sunday, residents reported.

On Tuesday officials said the fighters pushed their offensive to within 60 kilometres of Baghdad, briefly holding areas of Baquba, a short drive from the capital.

The overnight attack on Baquba, which was pushed back by security forces but left 44 prisoners dead at a police station, marked the closest that fighting has come to the capital as part of a lightning offensive in which jihadists have said they intend to march on Baghdad and the southern Shiite holy city of Karbala.

As the ISIL insurgents and the Sunni groups working with them tightened their grip on the north of the country, neighbouring Turkey warned the violence had the “potential to turn into large-scale sectarian clashes”, while the United States indicated it may hold talks with Iran on the escalating crisis in Iraq.

Turkey's state-run news agency Anadolu reported that the fighting in Tal Afar, a city of around 200,000 residents, had resulted in heavy civilian casualties.

And a statement released by the UN High Commissioner for Human Rights Navi Pillay said corroborated reports from a number of sources indicated the horrifying photographs of a mass execution of Iraqi soldiers released by ISIL on its Twitter feed over the weekend had been verified.

“It appears that hundreds of non-combatant men were summarily executed over the past five days, including surrendered or captured soldiers, military conscripts, police and others associated with the government,” Ms Pillay said.

“This apparently systematic series of cold-blooded executions, mostly conducted in various locations in the Tikrit area, almost certainly amounts to war crimes.”

Forces affiliated with ISIL also executed the Imam of the Grand Mosque in Mosul for refusing to pledge allegiance to the group, the UN said, while there were also reports that 12 local imams were allegedly executed in front of al-Israa mosque, also in Mosul, for the same reason.

As further evidence emerged of atrocities committed by ISIL and its co-insurgents and as the Iraqi Army stepped up its campaign of air strikes against the Sunni extremists, more and more Iraqis fled to the relative safety of the country’s semi-autonomous region of Kurdistan.

At the Khalak checkpoint between Mosul and Erbil, the Kurdish capital, hundreds of cars packed with families and their belongings squeezed into lanes six-wide in a rush to escape the renewed violence.

The Iraqi Ministry of Defence released images of air strikes on what it described as militant positions in Iraq, although many Iraqi civilians cited the air strikes as the main reason for leaving their homes.

“During the war in 2003 the planes came and bombed us, and now it is happening again – it is a sound we all dread,” said one woman, Amal, who did not want to her last name used.

The US Secretary of State, John Kerry, said US air strikes, including from unmanned drones may be an option for President Barack Obama, who is still weighing options following a request for assistance from Iraqi Prime Minister Nouri al-Maliki.

Air strikes "are not the whole answer, but they may well be one of the options that are important to be able to stem the tide and stop the movement of people who are moving around in open convoys and trucks and terrorising people," US Secretary of State John Kerry said.

"When you have people murdering, assassinating in these mass massacres, you have to stop that and you do what you need to do if you need to try to stop it from the air or otherwise."