At least three people were killed and four wounded when three mortar bombs hit the northern Iraqi town of Shirqat on Tuesday, police officials and hospital sources said.
Police officials in the area said ISIS militants were involved in the attack and the mortars were fired from a nearby mountainous area were militants are still active.
"Daesh (Islamic State) fighters are hiding in (the) Makhoul mountains area and use it as a launchpad for their attacks," said Shirqat police colonel Khalil Sahan.
ISIS has recently mounted a series of hit-and-run attacks aimed at undermining the government.
Iraq declared victory over the group, which once held large swathes of the country, in December 2017. But after they were defeated and driven out of areas they controlled for years, the militants have adapted their tactics to insurgent-style attacks.
Iraq's military announced a new operation on Sunday in an attempt to secure the vast western desert leading to the Syrian border, amid fears that ISIS sleeper cells were using the area to regroup.
The operation, dubbed "Will of Victory", began early Sunday morning and would push to clear the remote territory between the provinces of Salahaddin, Nineveh and Anbar, a statement by the military said.
Iraqi armed forces, paramilitary units of the Shiite-dominated Hashed Al Shaabi, tribal groups and US-led coalition warplanes were all taking part, according to the statement.
"There are pockets of Daesh fighters in the northwestern, western, and southwestern parts of Salahaddin province," a media official from the province's military command said, using the Arabic acronym for the group.
"Daesh is still present in these areas, and the operations will continue until they are cleared."