"Death to America," they chanted at a mass gathering in the streets of the southwestern city, where Soleimani's remains arrived from Iraq before dawn, according to semi-official news agency ISNA.

They beat their chests to the sound of Shiite chants and 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.

Soleimani was killed in a US drone strike Friday near Baghdad international airport that shocked the Islamic republic. He was 62.

The assassination, which was ordered by US President Donald Trump, ratcheted up tensions between the arch-enemies and sparked fears of a new war in the Middle East.

Iran's supreme leader Ayatollah Ali Khamenei vowed "severe revenge" and declared three days of mourning following the news of his death.

Trump warned on Saturday that America was targeting 52 sites in Iran and would hit them "very fast and very hard" if the Islamic republic attacks American personnel or assets.

In a sabre-rattling tweet, Trump said: "If they attack again, which I would strongly advise them not to do, we will hit them harder than they have ever been hit before!"

Tensions between longtime foes Iran and the US escalated last year when Trump unilaterally withdrew from a landmark accord that gave the Islamic republic relief from sanctions in return for curbs on its nuclear programme.

- 'Glorious crowd' -

On Sunday, thousands of mourners dressed in black were seen gathered in the southwestern Iranian city of Ahvaz in a live broadcast on state television.

The footage showed crowds gathered in Mollavi Square with flags in green, white and red -- depicting the blood of "martyrs".

Men and women wept as they beat their chests to the sound of Shiite 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.

"A glorious crowd is at the ceremony," said state television.

"The presence of children, teenagers, relatives, veterans, families of martyrs of (the Iran-Iraq war) and defenders of Haram (those martyred in Syria) is a glimpse of the glory of this ceremony," it added.

ISNA news agency said Soleimani's remains and those of five other Iranians -- all Guards members -- killed in the US drone strike 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.