The Islamic State jihadist group claimed to have executed 11 pro-government fighters in Iraq, in a series of photographs shared online on Tuesday.

The first picture shows masked men armed with assault rifles marching a line of orange jumpsuit-clad prisoners across a field.

The captives are then shown kneeling in front of the gunmen with their hands bound.

The final photographs show a row of bodies face-down in front of the militants with blood pooling on the ground.

Text accompanying the photographs said the men were killed in Salaheddin province, north of Baghdad, the scene of fierce fighting last month in which government forces recaptured its capital Tikrit.

Captions identified them as members of the Popular Mobilisation paramilitary units which have been fighting against the jihadists alongside the army.

The Islamic State group led an offensive last June that overran large areas north and west of Baghdad, sweeping security forces aside.

Baghdad turned to the Popular Mobilisation units -- which are dominated by Iranian-backed Shiite militias -- to bolster its flagging forces, and has since been able to regain significant ground from IS.

IS has carried out a string of atrocities including videotaped beheadings and mass executions, rape and enslavement in areas it controls in Iraq and neighbouring Syria.