BAGHDAD. The insurgent offensive that has threatened to dismember Iraq spread to the northwest of the country on Sunday, when Sunni militants launched a dawn raid on a town close to the Syrian border, clashing with police and government forces.

As the rapid advance south by the Islamic State in Iraq and the Levant (ISIL) towards Baghdad appeared to slow over the weekend, fierce fighting erupted in the town of Tal Afar 60 km west of Mosul near the Syrian border, security sources and a local official said.

ISIL fighters and other Sunni Muslim armed groups have stormed several towns on the road to Baghdad after seizing Mosul nearly a week ago - an offensive which only stalled as it approached the mainly Shi’ite capital.

The advance alarmed both Prime Minister Nuri al-Maliki’s Shi’ite supporters in Iran and officials in the United States, which helped bring him to power after its 2003 invasion that toppled Sunni dictator Saddam Hussein.

U.S. President Barack Obama said on Friday he was reviewing military options, short of sending troops, to combat the insurgency, and Iran held out the prospect of working with its longtime U.S. arch-enemy to help restore security in Iraq.

Maliki’s security forces and allied militias regained some territory on Saturday, easing part of the pressure on his Shi’ite-led government, and officials said they were regaining the initiative. Maliki has vowed to rout the insurgents.

But Sunday’s fighting in Tal Afar, a majority Turkomen town which is home to both Shi’ites and Sunnis, showed how volatile the deepening sectarian divisions have become.

Residents in Sunni districts accused Shi’ite police and army forces of launching mortar fire at their neighbourhoods, prompting ISIL forces stationed outside the town to move in.

"The situation is disastrous in Tal Afar. There is crazy fighting and most families are trapped inside houses, they can’t leave town,” a local official said. "If the fighting continues, a mass killing among civilians could result.”