BAGHDAD (AFP) - The Iraqi government will investigate allegations of abuses by the security forces in the course of the operation to retake the jihadist-held city of Fallujah, a spokesman said on Sunday (June 5).

Prime Minister Haider al-Abadi has ordered the creation of a human rights committee to examine "any violation to the instructions on the protection of civilians", Saad al-Hadithi said in a televised briefing.

He said Abadi had issued "strict orders" for prosecutions to take place in the event of any abuses.

Grand Ayatollah Ali al-Sistani, the most revered Shiite cleric in Iraq, has issued guidelines intended as a form of code of conduct for forces fighting the Islamic State of Iraq and Syria (ISIS) group and aimed at curbing abuses.

Officials including Parliament Speaker Salim al-Juburi have expressed concern over reports of abuses committed by the forces involved in the operation to recapture Fallujah.

Juburi spoke on Thursday of "information indicating that some violations were carried out by some members of the federal police and some volunteers against civilians".

The statement did not provide details on the alleged abuses, but urged Abadi to "look into these acts and deal with them in a strict and expeditious way".

Fallujah is a Sunni city that lies only 50 kilometres west of Baghdad and is one of ISIS's most emblematic bastions.

The Hashed al-Shaabi taking part in the Fallujah operation is an umbrella organisation that includes Sunni tribal fighters but is dominated by powerful Tehran-backed Shiite militias.

It is nominally under Abadi's authority but some of its most powerful groups answer directly to Iran.

Those groups have been repeatedly accused of fuelling sectarianism and their involvement in the Fallujah battle was seen as potentially explosive.

Hadithi reiterated Abadi's stance that the fate of the estimated 50,000 civilians still believed trapped inside the besieged city was given utmost priority.

"The operation to liberate Fallujah could have been completed in days but we put the safety of civilians first," the spokesman said.

Iraqi forces launched an offensive to retake the jihadist bastion on May 22 and 23. After a week of shaping operations, they have since struggled to break into the city centre.

The UN's top envoy in Iraq, Jan Kubis, also said in a statement that Iraq should "thoroughly investigate" reports of human rights violations against civilians.

"This noble cause of ridding Fallujah of Daesh (ISIS) terrorists should not be allowed to be tarnished by violations of human rights and dignity of people, notably on sectarian grounds," he said.