IRAQI government forces re-entered Kirkuk yesterday for the first time since 2014.

Peshmerga troops of the Kurdistan regional government (KRG) withdrew from the disputed city beforehand, with the KRG claims as part of its territory.

That withdrawal appeared to have avoided bloody clashes between the two sides, which had previously worked together to confront the Isis death cult which swept through northern Iraq three years ago.

But relations have become seriously fraught since the KRG held an independence referendum in late September in the areas it held. The Baghdad government condemned it as illegal.

The Peshmerga retreated from the city as the army rapidly surrounded the city and moved into its centre, raising the national flag.

Kurdish officials accused the army of staging a “major, multi-pronged attack” but state-backed militias instead said there had been little fighting.

The Peshmerga general command called it “a flagrant declaration of war against the nation of Kurdistan” and said Prime Minister Haider al-Abadi would pay a “heavy price” for it.

US-led Inherent Resolve coalition spokesman Colonel Ryan Dillon said he was “closely monitoring” the situation near Kirkuk, urging all sides to “avoid escalatory actions” and instead “finish the fight versus Isis — biggest threat to all.”

KRG president Masoud Barzani, who is accused of holding the independence referendum for cynical political reasons, was accused by Baghdad of asking for help from Kurdistan Workers Party (PKK) units.

It was not clear if that had happened, however, and the PKK has often been at odds with Mr Barzani’s Kurdistan Democratic Party.

KRG forces took over most of Kirkuk, Iraq’s richest oil-producing region, along with parts of Nineveh, Salah al-Din and Diyala provinces in 2014 following the sudden Isis offensive that overran a significant part of northern Iraq.

But it angered Baghdad, along with neighbouring Iran and Turkey, when it included those predominantly Arab or Turkmen areas in its unauthorised independence referendum last month.