University students abducted in the northern Iraqi city of Mosul Sunday have been released by the army, the defence ministry said.

All 42 students who were abducted by gunmen have been freed by Iraqi forces in an operation launched shortly after the kidnapping, the ministry source, who spoke on condition of anonymity, said.

Earlier Sunday, gunmen seized the students from the University of Mosul who were on a bus on the main highway between Baghdad and Mosul, the capital of the northern province of Nineveh.

Mosul, 400 km north of Baghdad, has been central stage for Sunni insurgents, who fled Baghdad and surrounding areas and regrouped in northern Iraqi provinces.

Baghdad has seen a relative calm credited mainly to a US troop operation and the involvement of tribal security units in fighting armed groups with links to the al-Qaeda terrorist network.

The Iraqi government has sent military reinforcements to Mosul after a significant surge in violence.