Iran's President Ebrahim Raisi vowed revenge against Donald Trump if the former US president is not tried over the killing of Qassem Soleimani, as Tehran marked two years since the commander's death.

"The aggressor and the main assassin, the then president of the United States, must face justice and retribution," Raisi said.

"It would be ok if the trial of Mr Trump, (former secretary of State Mike) Pompeo and other criminals was held in a fair court where their horrible crimes were addressed and they faced justice for their actions," he added.

"Otherwise, I will tell all US leaders that without a doubt the hand of revenge will emerge from the sleeve of the Muslim nation."

Raisi was addressing thousands at Tehran's biggest prayer hall, at Iran's main event to mark Soleimani's death anniversary during a week of commemorations.

Participants held national flags and portraits of the slain commander, state TV showed.

Raisi called Soleimani a symbol of the Iranian revolution and of "bravery and rationality".

Soleimani, former commander of the Quds' force, the foreign operations' arm of Iran's Revolutionary Guards, was killed along with his Iraqi lieutenant Abu Mahdi al-Muhandis, in a US drone strike near Bagdad's airport on January 3, 2020.

Five days later, Iran retaliated by firing missiles at a US airbase in Ain al-Assad housing American troops in Iraq, and another near Arbil in the north.

No US troops were killed in those strikes but Washington said dozens suffered traumatic brain injuries from the blasts.

Trump said at the time he had ordered the drone strike in response to a number of attacks on US interests in Iraq, and with more expected.

Iran's foreign ministry said in a Twitter post on Friday that "the current US government bears definitive international responsibility for this crime".