Iraqi forces take control of Kirkuk governor's office

The rapid advance - involving troops, tanks and armoured vehicles - aims to recapture oil and military targets captured by Iraqi forces during their fightback against the Islamic State group in 2014.

A source within the provincial administration said Kurdish Kirkuk governor, Najm Eddine Karim, was not there at the time the troops entered his office and the council building was empty.

Photos shared on social media showed pro-government troops in the governor's office highlighting the collapse of Kurdish defences in the city.

Earlier on Monday, Iraqi Prime Minister Haider al-Abadi assigned an Arab politician Rakan Saeed to replace Karim, sources told The New Arab. 

The move came after the Kirkuk governor called on residents to take to the streets and fight.

"We saw some of the young people who expressed their readiness to help their Peshmerga brothers to defend the land," Karim told Rudaw, a Kurdish media network.

The Iraqi parliament voted last month to remove Karim from his post over his strong endorsement of the controversial independence referendum, which was held in the city on 25 September. Karim had refused to step down.

On Monday, thousands of residents fled Kurdish districts, heading in buses and cars towards the autonomous Kurdistan region of northern Iraq. 

"We're leaving because we're scared there will be clashes" in the ethnically mixed city of 850,000 people, said 51-year-old Chounem Qader told AFP.

Iraqi and Kurdish Peshmerga forces exchanged artillery fire early on Monday south of the provincial capital, after the launch of the operation overnight which triggered a spike in oil prices on world markets.

Pumping stopped at Kirkuk's two main oil fields as Kurdish technicians halted operations and left the wells, an oil ministry official said.

A Kurdish health official said at least ten Peshmerga fighters were killed and 27 wounded during fighting overnight, but there was no confirmation of the toll from the Kurdish government. 

The rapid progress of Iraqi forces suggested that Kurdish fighters were withdrawing with little or no resistance in many areas.

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Iraq's Joint Operations Command said its forces had retaken the K1 military base north-west of Kirkuk, the military airport east of the city and the Baba Gargar oil field, one of six in the disputed region.

The US-led coalition against IS urged the two sides - both key allies - to "avoid escalatory actions" and to focus on fighting the jihadists, on the verge of losing their last strongholds in Iraq.

Agencies contributed to this report.