The Islamic State jihadist group beheaded an Iraqi soldier in Salaheddin province, north of Baghdad, according to a series of photos posted online on Wednesday.

It is the latest in a long series of atrocities committed by IS, which has killed thousands of people in territory it controls in Iraq and Syria and frequently documents the murders in grisly images shared by its supporters.

In one shot, three militants, two of them masked and a third holding the group's flag with his face uncovered, stand behind a fourth man dressed in an orange jumpsuit who is kneeling on a dirt road.

The next shot shows the victim lying on his side with his hands bound as one of the masked men kills him with a knife, while the last pictures his head sitting atop his body next to a photo apparently showing him dressed in a camouflage army uniform.

The series of photos, the authenticity of which could not be independently confirmed, were said to have been taken near the town of Baiji, an area that has seen heavy fighting between IS and pro-government forces.

IS spearheaded a militant offensive that swept security forces aside and overran large areas north and west of Baghdad in June.

Iraqi security forces, backed by Kurdish troops, Shiite militias, Sunni tribesmen and a US-led campaign of air strikes, have managed to regain some ground from IS.

But significant territory, including three major cities, are still controlled by the brutal jihadist group.