Gunmen killed two policemen and security forces discovered the corpse of a Christian woman stabbed to death in Iraq's main northern city on Monday, officials said.

The two policemen were killed and three others wounded when militants opened fire on their checkpoint in Mosul, 350 kilometres (220 miles) north of Baghdad, while the woman's body was found in her apartment, police and a doctor said.

Despite dramatically lower levels of violence nationwide, Mosul and surrounding Nineveh province remain one of Iraq's most violent areas, accounting for nearly a fifth of all civilian deaths in 2012 according to the Iraq Body Count monitoring group.

The city is widely seen as one of the few in Iraq where Al-Qaeda-linked militants hold significant sway, and shootings and murders are commonly attributed to its front group, the Islamic State of Iraq.