The January 3, 2020 strike killed revered Iranian General Qasem Soleimani -- who headed the Quds Force, the foreign operations arm of Iran's Revolutionary Guards -- and Hashed deputy Abu Mahdi al-Muhandis.

The Hashed is an Iran-aligned group that began life as a paramilitary force, before being integrated into Iraq's security forces.

The night-time strike, ordered by then US president Donald Trump, hit a car in which Soleimani and Muhandis were travelling on the edge of the airport. The burnout shell of the vehicle remains displayed there.

On Sunday evening, hundreds of Hashed supporters, including men and women who brought children, gathered at the site, to pay tribute to the slain men.

Holding pictures of Soleimani and Muhandis and Hashed flags, they lit candles that they left by the vehicle, an AFP photographer said.

Thousands of Hashed supporters had on Saturday gathered in central Baghdad for initial commemorations.

The US said at the time that Soleimani was planning imminent action against US personnel in Iraq, a country long torn between the competing demands of its principal allies Washington and Tehran.

Five days after his killing, Iran fired missiles at an air base in Iraq housing US troops and another near Arbil in the country's north.

Since then dozens of rockets and roadside bombs have targeted US security, military and diplomatic sites across Iraq.

Western officials have blamed hard-line pro-Iran factions for the attacks, which have never been claimed by any group.

The Hashed has repeatedly called for the withdrawal of US troops deployed in Iraq as part of a multinational coalition fighting Islamic State group jihadists.

Iran is due to hold its own main annual commemorations of Soleimani's killing on Monday.