Islamic State militants attacked a power station and other buildings in the northeastern Iraqi oil city of Kirkuk early on Oct. 21, killing at least 18 people, security sources said. Crude oil production facilities were not targeted and the power supply continued uninterrupted in the city, the sources said.

Islamic State claimed responsibility for the attacks in online statements as Kurdish Peshmerga reinforcements arrived in the city.

The assailants in Kirkuk came from outside the city, said the head of Iraq's Special Forces, Lieutenant General Talib Shaghati, speaking on a frontline east of Mosul.

Fighting raged on through the afternoon as authorities called a curfew, saying some of the attackers were still holed up in a hotel and a mosque in the middle of the city that is currently held by Kurdish Peshmerga fighters.

The attacks came four days after Kurdish and Iraqi forces started an offensive more than 170 kilometers (km), or 100 miles, farther north to push Islamic State out of Mosul, the militants' last major city stronghold in Iraq.

It was not immediately clear if the militants had attacked Kirkuk in response to the ongoing fighting in Mosul.

Bursts of machine gun fire could be heard on video footage of the two-floor abandoned hotel in Kirkuk. Cars burned nearby, filling the street with black smoke.

Most of the dead there were members of the security forces and workers at the power station, including two Iranians who were performing maintenance, the security sources said.

At least eight militants were also killed, either by blowing themselves up or in clashes with the security forces, the sources added. Some of the surviving militants cut the road between the city and the power station, 30 km farther north.

Kurdish Peshmerga fighters took control of Kirkuk in 2014, after the Iraqi army withdrew from the region, fleeing an Islamic State advance through northern and western Iraq. The hardline group also controls part of neighboring Syria.