Thousands of mourners swept into the Iranian city of Ahvaz early on Sunday morning to receive the remains of Qasem Soleimani, the general killed in a US drone strike in Baghdad last week.
The mourners beat their chests and chanted “death to America”.
Soleimani was the architect of Iran’s sphere of influence across the Middle East and he was considered to be the country’s second most powerful man.
His assassination marked a significant escalation between Iran and the US.
Iran’s supreme leader, Ayatollah Khamenei, who had a close personal relationship with Soleimani, warned of “severe revenge” for the attack, and analysts said Iran might pursue cyber attacks against the US or traditional attacks on US targets or interests in the Middle East.
President Trump, who authorised the attack on Soleimani on Friday – an option refused by both Presidents Bush and Obama as too risky – said on Saturday the US was ready to strike 52 sites “important to Iran & the Iranian culture”.
In a series of tweets likely to raise concerns about a path to war between the two countries, Mr Trump said the US would strike Iran “VERY FAST AND VERY HARD” if Iran targeted American bases or troops.
The president said the 52 targets identified by the US represented 52 Americans who were held hostage in Iran for more than a year from late 1979 after they were taken from the US embassy in Tehran.