TIKRIT, Iraq (Reuters) - Islamic State militants killed three government-backed militia fighters on Monday near Iraq’s biggest oil refinery in the northern city of Baiji, police and militia sources said.

Iraq declared victory in December over Islamic State, which had seized control of nearly a third of the country in 2014, but it continues to carry out attacks and bombings in Baghdad and other parts of Iraq.

Police sources said at least seven militants opened fire on the militia forces in Baiji. Four of the attackers were killed and at least two others were still at large, they said.

A security official said some of the militants were identified as wanted Islamic State members.

At least five other fighters from a government-affiliated militia known as Popular Mobilisation Forces (PMF) were critically wounded, a local militia commander said.