US Secretary of State John Kerry has urged the leaders of the state’s autonomous Kurdish region to join Baghdad in forming an inclusive government.

Kurdish troops have seized on the conflict in the north of the country to expand their territory. They have reportedly taken control of rich oil deposits, as well as Kirkuk, a city they consider their historic capital.

Under Iraqi Kurdish President Massoud Barzani, officials have made it clear the resolution keeping Iraq together as a state is in danger.

But Kerry appealed for unity.

“In recent days the security cooperation between the forces here, in the Kurdish area, have been really critical in helping to draw a line in respect to ISIL,” he said.

Washington’s plea comes as militants from the Islamic State of Iraq and the Levant (ISIL) take over more cities in the north.

The strategically-placed Baiji oil refinery has been fought over for almost a week.

Although the Ministry of Defence released a video claiming to show Iraqi forces thwarting an attack on the plant, Baghdad still appears to be struggling to secure its grip on Sunni provinces.