Two Iranian Revolutionary Guardsmen were killed by a US 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.

Pictures of the two men, named as Ali Yazdani and Hadi Jafari, were posted on Iranian news websites after their funerals on home soil.

The Fars news agency called Jafari, 29, the third "martyr in defence of the shrines" from the northern Iranian city of Amol. Yazdani was buried in Tehran, it reported.

Iran, the predominant Shiite Muslim power in the Middle East, has said it is supporting ally Iraq and will protect its Shiite holy places against IS.

However, the US Department of Defense said in a statement that it had not conducted air strikes in the Tikrit area on the date the men were said to have been killed.

"Coalition forces initiated air strikes near Tikrit on March 25, two days after the alleged incident occurred and no air strikes were conducted in or near Tikrit on March 23," said Major Omar Villarreal, a spokesman for US Central Command.

"We have no information to corroborate claims that coalition air strikes killed two IRGC members," he added, referring to Iran's Islamic Revolutionary Guard Corps.

Iranian-backed Shiite militia groups have for weeks been heavily involved in fighting in Tikrit, seeking to reclaim the city, the home of the executed Iraqi dictator Saddam Hussein, from IS.

Iranian media have reported the deaths of military personnel, including several generals, killed in Iraq and Syria after Tehran sent them in support of Baghdad's government and of Syrian President Bashar al-Assad in conflicts against IS and Sunni rebels.

Iran denies its troops are fighting on the ground in Iraq and Syria, but Tehran has said it has military advisers in both countries.

Other Iranians have joined Shiite militia groups as volunteers.

The Revolutionary Guard, however, is integral to the fighting in Iraq.

Major General Qassem Suleimani, who leads the Quds Force, the Guard's foreign wing, has been pictured on social media near the frontline in Tikrit and other battlegrounds, where he is said to be coordinating Shiite militia groups.

Other Revolutionary Guard deaths have included General Mohammad Ali Allahdadi, killed along with six fighters of Lebanese Shiite militant group Hezbollah in an Israeli air strike in Syria on January 18.

Brigadier General Hamid Taghavi, also a member of the Guard, was killed in the Iraqi city of Samarra north of Baghdad in December while advising Iraqi troops.

Suleimani was pictured at a funeral ceremony for Taghavi.