Iraq is to test the body of a man killed on Friday by pro-government forces to determine if it is that of Saddam Hussein's long-fugitive deputy Izzat Ibrahim al-Douri.

Douri was vice president at the time of the 2003 U.S.-led invasion.

Iraq has exhumed the remains of 164 people believed to have been massacred by jihadists from mass graves in Tikrit, the human rights ministry said Monday.

"Search teams have discovered the remains of 164 (victims) so far in four mass graves during work over the past week," ministry spokesman Kamel Amin told AFP.

Exploding bombs send clouds of dust rising into the air over the Iraqi city of Tikrit, houses and businesses burn and civilians are nowhere in sight.

Iraqi forces have retaken Tikrit from the Islamic State (IS) group after a month-long operation, but the task of returning some semblance of normal life to the city will take far longer.

Pro-government militiamen were seen looting shops in the center of the Iraqi city of Tikrit on Wednesday after retaking it from the Islamic State jihadist group in a month-long battle.

The militiamen took items including clothing, shampoo and shaving cream from two shops in central Tikrit before driving away, witnesses said.

Iraqi forces which retook Tikrit from the Islamic State group found burial sites Wednesday believed to hold victims of a June massacre in which hundreds of army cadets were executed.

The Speicher massacre -- named after the nearby base from which the mostly Shiite recruits were abducted -- stoked widespread anger against IS and helped rally support to battle the jihadists.

Two Iranian Revolutionary Guardsmen were killed by a U.S. drone in the Iraqi city of Tikrit, Iranian state media said Monday, in a report that was denied by the Pentagon.

The official IRNA news agency said the two had been posted to Iraq as advisers in the war against Islamic State (IS) group jihadists and that they died in the drone strike on March 23.

Retaking the city of Tikrit, where jihadists have rigged streets and buildings with explosives, will require "major sacrifices" on the part of Iraqi forces, a senior intelligence officer said Saturday.

Iraqi forces and allied paramilitaries have been fighting to retake the city since March 2, but halted ground operations for more than a week in what officials described as a bid to curb human and material losses before pushing forward again.

Iraq's Shiite militias have withdrawn from the forefront of an offensive to recapture Tikrit from Islamic State jihadists, allowing Baghdad government troops to take the lead, a top U.S. general said Thursday.

The Shiite militias "have pulled back from that area" and Iraqi special forces and police are clearing Tikrit, General Lloyd Austin, head of U.S. Central Command, told lawmakers.

Air strikes by the U.S.-led coalition would help win the battle to retake the Iraqi city of Tikrit from the Islamic State group, one of the operation's commanders said Sunday.

Staff Lieutenant General Abdulwahab al-Saadi said he had asked the defense ministry to request coalition involvement but "no air support was provided."

Iraqi forces faced tough resistance from jihadist fighters around Tikrit Saturday but the top U.S. military officer said ahead of a visit to Baghdad victory was only a matter of time.

Iran has actively and visibly supported Baghdad's biggest operation yet against the Islamic State group but General Martin Dempsey insisted U.S. air strikes north of Tikrit had been key.