Gunmen have killed at least 42 soldiers in separate attacks in the Iraqi cities of Fallujah and Mosul.

Police sources told Al Jazeera that 22 soldiers who had been kidnapped in Fallujah on Friday were killed on Saturday night.

In a separate incident, fighters kidnapped troops from a small base in Ain al-Jahash, south of Mosul, on Saturday, and later shot them dead, police sources said on Monday.

Their bodies were found an hour after the initial attack.

A medical official, who confirmed the casualty number in the Ain al-Jahash attack, said 11 troops had their hands tied behind their backs and suffered close-range gunshots to the head, the AP news agency reported.

Fighters opposed to the Iraqi government frequently target members of the security forces, but it is rare such large number of soldiers to be kidnapped at once, especially from a military facility.

The killings come as the country suffers a protracted surge in bloodshed, the worst the country has experienced since the brutal sectarian fighting that peaked in 2006-2007 and killed tens of thousands of people.

The government has blamed the upsurge in violence on external factors, such as the civil war in Syria, but analysts say there is also widespread resentment among the Sunni Arab community over alleged mistreatment by the Shia-led government.

The government has been involved in heavy fighting with rebels in Fallujah, where groups including the Islamic State of Iraq and the Levant have a foothold.

Mosul, a former stronghold of groups fighting the central government and US occupation, is located 360km northwest of Baghdad.

Source: Al Jazeera and agencies