(CNN) — ISIS militants attacked several security buildings in the Iraqi city of Kirkuk, officials said, even as Iraqi and Kurdish forces battle the terror group for control of the second-largest city of Mosul.
Dozens of militants targeted four police stations and Kurdish security offices in Kirkuk, spreading themselves out through several residential neighborhoods. The clashes were ongoing in the southern part of the city as of Friday morning, security officials said.
A number of people were killed and wounded, but officials could not provide an exact figure. Images broadcast on local television showed what appeared to be dead or injured fighters on the street.
Local authorities imposed a curfew in Kirkuk amid the attacks.
Kirkuk is 175 kilometers (109 miles) southeast of Mosul, where a major military offensive has been under way this week.
Kirkuk has been attacked before by ISIS militants. Previous attacks have been seen as attempts by ISIS to either capture the city or divert Kurdish troops from the fight in Mosul.
The most likely reason for Friday’s assault is disruption, with ISIS demonstrating it can deploy its resources far behind the front lines, CNN’s Michael Holmes said near Mosul.
“It’s long been thought that there would be something like this going on in more than one place around Iraq as the Mosul offensive got under way,” he said. “There’s been speculation that there are ISIS sleeper cells, or ISIS fighters, within reach of places like that for some time, from Baghdad to places like Kirkuk.”
The city’s significance stems from the fact its oil reserves are almost as much as those in southern Iraq.
Kirkuk is 378 kilometers (235 miles) north of Baghdad and has seen ISIS fighters pitted against the Peshmerga, Iraqi government troops and an international coalition.
Intense battle around Mosul
Fighting around Mosul was fierce Thursday,
Peshmerga forces ‘ command said they advanced “significantly” to the north and northeast of Mosul on Thursday, and liberated a number of villages.
However, it criticized the air support provided by the international coalition, saying it was “not as decisive as in the past.”
“Regrettably a number of Peshmerga have paid the ultimate sacrifice for us to deliver today’s gains against ISIL,” it said, using another acronym for ISIS. Up to 10,000 Peshmerga are involved in the operation on three fronts, it said.
The US envoy for the anti-ISIS coalition, Brett McGurk, said via Twitter that he was heading to Irbil on Friday to meet with US, Iraqi, and Kurdish officials taking part in the Mosul campaign.
The Pentagon announced late Thursday that a US service member died of injuries suffered during a blast in northern Iraq.
In a separate incident, ISIS militants also attacked a government building in Dibis town, about 40 kilometers (25 miles) northwest of Kirkuk on Friday.
Twelve people were killed in the attack, including nine Iraqi employees and three Iranian contractors, two security officials told CNN.