One person was killed and at least 24 wounded when bombs hit two crowded passenger buses in Iraq’s oil-rich city of Kirkuk on Thursday, officials said.

The two devices exploded as the buses drove through the city center around 7 p.m. (1600 GMT), police sources said.

There was no immediate claim of responsibility, but Iraq’s military called the blasts an act of terrorism.

Islamic State has mounted a series of hit-and-run attacks aimed at undermining the government.

Iraq declared victory over the militants in December 2017, but they have regrouped in the Hemrin mountain range in the northeast, which extends from Diyala province on the border with Iran across northern Salahuddin province and into southern Kirkuk.

On Tuesday, four Iraqi federal policemen were killed after a bomb went off southwest of Kirkuk, two security sources said.

It followed an attack on Monday on a village 65 km (40 miles) southwest of Kirkuk, which killed three residents.