Islamic State (IS) militants have killed at least 14 people after launching a wave of pre-dawn attacks in and around the northern Iraqi city of Kirkuk on Friday.
The assault appeared aimed at diverting attention from the Iraqi offensive to retake Mosul and raised fears the extremists could lash out in unpredictable ways as they defend the largest city under their control and their last urban bastion in Iraq.
Multiple explosions rocked Kirkuk and gunfire rang out around the provincial headquarters where the fighting was concentrated.
Smoke billowed over the city and the streets were largely deserted out of fear of militant snipers.
IS said its fighters targeted the provincial headquarters in a claim carried by its Aamaq news agency.
North of the city, three suicide bombers stormed a power plant in the town of Dibis, killing 13 workers, including four Iranian technicians, before blowing themselves up as police arrived, said Major Ahmed Kader Ali, the Dibis police chief.
Iran's Foreign Ministry spokesman Bahram Ghasemi condemned the assault, which he said also wounded three Iranian workers, according to the official IRNA news agency. It was not immediately clear if Iranians were targeted in other attacks.
The Turkmeneli TV station, which had earlier shown live footage of smoke rising from outside the provincial headquarters, said in a news bulletin one of its reporters, Ahmet Haceroglu, was killed by a sniper while covering the fighting.
There was no immediate word on casualties among other civilians or the Kurdish forces in Kirkuk. Police and hospital officials could not be reached for comment.
Kirkuk is some 100 miles from the IS-held city of Mosul, where Iraqi forces launched a wide-scale offensive on Monday.
IS has in the past resorted to suicide bombings in and around Baghdad in response to battlefield losses elsewhere in the country.
Kurdish forces assumed full control of Kirkuk in the summer of 2014 as Iraq's army and police crumbled in the face of a lightning advance by IS.
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, but that his forces repelled the assault.
Iraqi and Kurdish forces backed by a US-led coalition launched the multi-pronged assault this week to retake Mosul and surrounding areas - the largest operation undertaken by the Iraqi military since the 2003 US-led invasion.
Elsewhere in Iraq, the country's top Shiite cleric called on forces taking part in the Mosul offensive to protect civilians, and for residents of Mosul, a mainly Sunni city, to co-operate with security forces.
"We stress today upon our beloved fighters, as we have before on many occasions, that they exercise the greatest degree of restraint in dealing with civilians stuck in the areas where there is fighting," the reclusive Grand Ayatollah Ali al-Sistani said in a Friday sermon read by an aide.
"Protect them and prevent any harm to them by all possible means."