Islamic State militants wielding assault rifles and explosives have attacked targets in and around the northern Iraqi city of Kirkuk.
The assault is apparently aimed at diverting security forces from a massive offensive against the IS-held city of Mosul.
At least 11 workers, including two Iranians, were killed when militants stormed a power plant north of Kirkuk and then blew themselves up on Friday morning.
Multiple explosions meanwhile rocked the city and gun battles were ongoing, witnesses said.
Much of the fighting was centred on a government compound in the city. They said the streets were largely deserted out of fear of militant snipers.
IS said its fighters targeted the provincial headquarters. 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.
It quoted Kirkuk Governor Najmadin Karim as saying the militants had 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 Major Ahmed Kader Ali, the Dibis police chief.
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, Ali said.
Kirkuk is about 170 kilometres from the Islamic State-held city of Mosul, where Iraqi forces have been waging a wide-scale offensive since Monday.