Ceremonies to honour top Iranian commander Qasem Soleimani, who was killed in a US air strike in Baghdad, began Sunday in Ahvaz, where his remains arrived from Iraq.
State television started a live programme showing thousands of mourners dressed in black gathered in the southwestern Iranian city.
The footage showed crowds gathered in Mollavi Square with flags in green, white and red — depicting the blood of "martyrs".
They held up portraits of the general, seen as a hero of the 1980-88 Iran-Iraq war and for spearheading Iran's Middle East operations as chief of the Revolutionary Guards' Quds Force.
Men and women wept as they beat their chests to the sound of Shia Muslim chants.
Aerial footage showed a tide of mourners crammed into Mollavi Square and the surrounding streets of downtown Ahvaz, a city of 1.3 million people.
Semi-official news agency ISNA said Soleimani's remains had arrived at Ahvaz airport before dawn.
They are expected to be flown to the Iranian capital for more tributes on Sunday evening.
On Monday, supreme leader Ayatollah Ali Khamenei is expected to pray over his remains at Tehran University before a procession to Azadi Square.
His remains are then due to be taken to the holy city of Qom for a ceremony at Masumeh shrine, ahead of a funeral in his hometown Kerman on Tuesday.