IRAQ - Kurdish authorities tightened security at checkpoints in Irbil on Tuesday, as thousands of Iraqi refugees fled from the northern city of Mosul to Kurdistan.

The autonomous Kurdish region in the north has its own armed forces, and on Tuesday the region's government suggested its willingness to intervene beyond the formal borders of the self-rule enclave.

The Mosul region lies on Kurdistan's doorstep, has a significant Kurdish population, and the Kurds claim parts of the area as part of the autonomous region.

"We protected and saved thousands of people who came from Mosul at the checkpoint and we have decided to build a camp for those people," said the governor of Irbil, Nawzad Hadi.

Islamist militants overran much of Mosul, Iraq's second largest city, on Tuesday seizing the governor's headquarters and rampaging through police stations, military bases and the airport as security forces collapsed and abandoned their posts.

The assault was a heavy defeat for Prime Minister Nouri al-Maliki in the face of a widening insurgency by a breakaway al-Qaida group, the Islamic State of Iraq and the Levant.

The group has been advancing in both Iraq and neighbouring Syria, capturing territory in what appears to be a campaign to set up a militant enclave straddling the border.