Militants armed with assault rifles and explosives attacked targets in and around the northern Iraqi city of Kirkuk early on Friday in an assault quickly claimed by the Islamic State group and likely aimed at diverting authorities' attention for the battle to retake IS-held Mosul.
At least 11 workers, including two Iranians, were killed when IS militants stormed a power plant north of Kirkuk and then blew themselves up.
Multiple explosions meanwhile rocked the city and gun battles were underway, said witnesses in Kirkuk, speaking on condition of anonymity as they were concerned for their safety. Much of the fighting was centered on a government compound in the city.
IS said its fighters were behind the attack, which the extremist group said targeted the Iraqi government. The claim was carried by the IS-run Aamaq news agency and could not immediately be verified.
Local Kurdish television channel Rudaw aired footage showing black smoke rising over the city as extended bursts of automatic gunfire rang out. The TV, however, quoted Kirkuk Gov. Najmadin Karim as saying that the militants have not seized any government buildings.
In the power plant attack, which took place in Dibis, a town north of Kirkuk, three IS suicide bombers entered the facility and took 10 workers hostage, said Maj. Ahmed Kader Ali.
The attackers asked to be taken to the Iranians who worked at the plant. One of the workers took them to the Iranians before escaping. The militants then killed the Iranians and the other workers, and detonated their explosive vests when police arrived.
Kirkuk is some 170 kilometers (100 miles) from the Islamic State-held city of Mosul, where Iraqi forces have been waging a wide-scale offensive since Monday.
The oil-rich city is some 290 kilometers (180 miles) north of Baghdad and southeast of Mosul. It is claimed by both Iraq's central government and the country's Kurdish region. It has long been a flashpoint for tension and has been the scene of multiple attacks by Islamic State militants.
Later Friday, Rudaw TV said all IS militants who took part in the Kirkuk attack had been killed except for two who were holed up in a newly built hotel, which was damaged in the attack and from where they were battling Kurdish forces.
There was no immediate word on casualties among civilians or Kurdish forces in Kirkuk and the TV report could not immediately be independently confirmed.
Kemal Kerkuki, a senior commander of Kurdish peshmerga forces west of Kirkuk, said the town where his base is located outside the city also came under attack early on Friday. He said the base is now under control.
He said IS maintains sleeper cells in Kirkuk and the surrounding villages, and that a group of IS fighters tried to attack a power station in Dibis village west of Kirkuk with light arms and a suicide bomber.
IS also claimed an attack on the power station, saying that its fighters had stormed the facility and killed all security forces stationed there.
Kerkuki said he believes the attackers infiltrated Kirkuk posing as displaced civilians. The city has absorbed hundreds of thousands of displaced people from neighboring provinces since IS first overran wide stretches of northern and western Iraq in the summer of 2014.
"Many of (the displaced civilians), I'm sure they are working with ISIS," Kerkuki said, using an alternative acronym for the Islamic State group. "We arrested one recently and he confessed (he was part of a sleeper cell)."
Iraqi and Kurdish forces backed by U.S.-led coalition support launched a multi-pronged assault this week to retake Mosul and surrounding areas from IS. The operation is the largest undertaken by the Iraqi military since the 2003 U.S.-led invasion.
Iraqi officials said they had advanced as far as the town of Bartella, 15 kilometers (9 miles) from Mosul's outskirts, by Thursday.