The Islamic State group beheaded an Iraqi police officer and two soldiers, the latest in a long series of atrocities committed by the jihadists, according to pictures posted online Sunday.

In one photo, a blindfolded man said to be a police lieutenant colonel kneels in a street in front of a row of gunmen.

A masked militant is then shown beheading the victim with a machete, after which his severed head is placed atop his body and the machete driven into his back.

Another photo shows an overweight masked militant apparently struggling to behead a man identified as a captured Iraqi soldier.

A second soldier was beheaded at the same location, according to another photo of the scene.

The authenticity of the photos could not be independently confirmed.

IS spearheaded a sweeping militant offensive in June that overran large areas north and west of Baghdad, and also holds significant territory in neighbouring Syria.

The brutal militant group has killed thousands of people in both countries, some of them in highly-choreographed videotaped sequences in which the victims are beheaded.

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 the jihadists still control significant territory, including three major cities.

Suicide bomber kills prominent tribal leader in Iraq
Baghdad (AFP) Jan 31, 2015 - A suicide bomber killed a prominent tribal leader and five other people in an attack southwest of Baghdad, police said on Saturday.

The bomber blew up a tanker truck rigged with explosives outside the home of Sheikh Lorens al-Hadhal in the Al-Nikhaib area of Anbar province on Friday night, Major Alaa al-Dulaimi said.

A former member of parliament, the sheikh was head of the powerful Aniza tribe, which has members in neighbouring Kuwait and Saudi Arabia as well as in Iraq.

The blast also wounded 14 people, Dulaimi said.

There was no immediate claim of responsibility for the attack, but suicide bombings are a tactic almost exclusively employed by Sunni extremists in Iraq, including jihadists of the Islamic State group.

IS spearheaded a lighting offensive that overran much of the Sunni Arab heartland north and west of Baghdad last June.

The country's powerful tribes are key to the government's efforts to retake and maintain control of areas currently held by the jihadists.