Smoke billows as Iraqi forces advance towards the centre of Kirkuk during an operation against Kurdish fighters on October 16, 2017.

:: The United States is “deeply concerned” about reports of violence around Kirkuk in Iraq, the spokesperson of the US Department of State said.

“We are watching the situation closely and call on the various parties to coordinate military action and restore calm,” spokesperson Heather Nauert said in a statement.

Iraqi government forces captured the major Kurdish-held oil city of Kirkuk on Monday, responding to a Kurdish referendum on independence with a bold lightning strike that transforms the balance of power in the country.

A convoy of armored vehicles from Iraq’s elite US-trained Counter-Terrorism Force seized Kirkuk’s provincial government headquarters less than a day after the operation began, a Reuters reporter in Kirkuk said.

Neither side gave a casualty toll for the operation. But an aid organization working in Kirkuk said several Kurdish Peshmerga fighters and members of the Iraqi forces had been killed in an overnight clash south of Kirkuk – the only serious fighting reported.

The statement from the Nauert also said that the US supports “the peaceful exercise of joint administration by the central and regional governments, consistent with the Iraqi constitution, in various disputed areas.”

“We are working with officials from the central and regional governments to reduce tensions, avoid further clashes and encourage dialogue,” she said.

She urged all parties involved to avoid provocations that could be exploited by “the enemies of Iraq who wish to fuel ethnic and sectarian conflict.”