The Kurdistan Regional Security Council (KRCG) issued its own statement saying Iraqi forces and Iranian-backed Popular Mobilization Forces advanced from Taza Khormatu in Kirkuk, just over 20 kilometers (12 miles) southwest of the city.
The council said Peshmerga forces were attacked using "US military equipment, including Abrams tanks and Humvees." It added the Peshmerga had destroyed a number of those Humvees.
The US-led coalition against ISIS (Operation Inherent Resolve) says it's closely monitoring the situation and is urging all sides to "avoid escalatory actions." Earlier, the Pentagon echoed this stance.
A long contentious city
Iraqi forces fled Kirkuk in 2014 as ISIS fighters attempted to secure the territory, shortly after taking over the city of Mosul and establishing their so-called Islamic caliphate across the northwest of the country.
The Kurds, however, sent in their fighters and claimed the city. It's been in their hands ever since, along with other disputed areas they took over when their fighters routed the Islamic State.
Baghdad wants the oil-rich city back, but the Kurds are refusing to return it. Both the Iraqis and the Kurds are US allies in the fight against ISIS.
On Twitter, Iraqi Prime Minister Haider al-Abadi called on citizens in Kirkuk to cooperate with Iraqi security forces, who he has directed to enter the city to impose security and provide protection for Kirkuk's residents.
Days earlier, he sought to downplay talk of impending clashes between Iraqi and Kurdish forces in the city. "Our armed forces cannot and will not attack our citizens, whether Arab or Kurd. The fake news being spread has a deplorable agenda behind it," he tweeted on Friday.
The Iraqi Joint Operations Command warned armed groups in Kirkuk against firing at Iraqi forces, Iraqi state TV reported.
According to a spokesman for Masoud Barzani, the president of the Kurdish Regional Government, the Kurdish fighters known as the Peshmerga are ordered not to "initiate any war, but if any advancing militia starts shooting, then Peshmerga are given a green light to use every power to stand against them.
Senior adviser Hemin Hawrami tweeted early Monday that "thousands of volunteers from other cities of Kurdistan are pouring in to Kirkuk." He accused al-Abadi of starting a war by using the Shiite militia units on Kirkuk. "He should wait, Kurdistan reaction will be much stronger than they expected."
Units of Iraqi forces have moved from the villages of al-Basheer and Taza and are approaching the city of Kirkuk, but no forces have entered the city so far, said Mahmoud Haji Mahmoud, commander of the Peshmerga forces in western Kirkuk.
He said advancing Iraqi troops are within one kilometer (0.62 miles) of the perimeter of the city and are setting up berms to use bulldozers near Peshmerga positions.
Three soldiers within the advanced Iraqi Counter Terrorism Forces told CNN that the Iraqi units been given orders to advance towards the south and west of the city's perimeter, secure entrances and take over a number of vital facilities located in that section.
The Iraqi forces consist of members of Shiite militias operating under the Popular Mobilization Units (PMU), along with Iraqi army forces.
The Kurdish regional security council tweeted on Sunday that Iraqi forces and the PMU were intending to take over a military base and major oil fields. The province has one of the biggest oil fields in the country, more than 6% of the world's oil comes from the Kirkuk region.
Kirkuk was historically a Kurdish-majority Iraqi town, but during his rule ousted dictator Saddam Hussein moved Arab families in and Kurdish families out to change the area's ethnography, under a policy termed "Arabization." It's also home to Sunni Arabs and Turkmen.
The city had suffered a series of major attacks over the past decade from extremists including al Qaeda in Iraq, targeting mostly security forces there.
After the fall of Saddam, Kurds began returning to Kirkuk, repopulating the city and its surrounding areas in the event of an eventual referendum on whether the city should be part of a future Kurdistan or remain in Iraq.
The Kurds last month voted overwhelmingly for independence from Iraq. In response, Baghdad shut down overseas flights to the KRG's international airports. The Kurds are holding firm however, and the status of Kirkuk is as much in doubt as ever.
CNN
