At least 56 mourners have been killed in a stampede, causing the burial of Iran's top military commander to be postponed, Iran's state television has reported.
More than a million people were on the streets for the funeral procession of Qassem Soleimani, who was killed in a US airstrike near Baghdad airport on Friday.
The stampede in the general's hometown of Kerman has also left 213 people injured. He was due to be buried in a "martyrs' cemetery" today.
It is not now clear when Major General Soleimani's burial will now take place.
As mourners gathered in Kerman, the semi-official Fars news agency reported that a top Iranian security official said Tehran is considering 13 "revenge scenarios" following the drone strike on the general.
Ali Shamkhani, secretary of the Supreme National Security Council of Iran, said: "The Americans should know that until now 13 revenge scenarios have been discussed in the council and even if there is consensus on the weakest scenario carrying it out can be a historic nightmare for the Americans."
Meanwhile, a senior Iranian official has said the country is "ready to come back to full compliance" in the nuclear agreement it has with a group of world powers.
Deputy foreign minister Abbas Araqchi did not provide any information on possible conditions.
Although Donald Trump has defended the US attack, the fury generated by Maj Gen Soleimani's death in both Iran and Iraq has led to the US-led coalition scaling back its operations in Baghdad.
American soldiers are set to be "repositioned" after Iraq's parliament called for all 5,000 US troops to leave the country - and a letter seen by Reuters suggests the US will move its forces over the "coming days and weeks".
However, US Defence Secretary Mark Esper said there had been "no decision whatsoever to leave Iraq".
Sky News correspondent Mark Stone said: "We understand around 1,100 forces in the green zone in Baghdad will be thinned out by a half or so.
"Some will be relocated within in Iraq, others in Kuwait.
"The plan we're told is that at some stage they will come back. The rest of the coalition forces in Iraq will remain."
Reuters says the letter is from William H Seely III, the American commander of Task Force Iraq, and that it has been independently verified.
Top US general Mark Milley, chairman of the Joint Chiefs of Staff, also sought to play down the letter, saying it was poorly worded and incorrectly implied withdrawal, when it was only meant to draw attention to increased troop movements.
Canada has confirmed it will temporarily move some troops from Iraq to Kuwait for safety reasons. Germany is also moving some troops out.
The leader of Iran's Revolutionary Guard has threatened to "set ablaze" places supported by the US over the killing of Maj Gen Soleimani.
He said Maj Gen Soleimani represented an even greater threat to Iran's enemies as a martyr, including to the country's longtime regional enemy Israel.
Mr Salami said: "We will take revenge. We will set ablaze where they like."
His words drew cries of "death to Israel".
Mr Salami's vow mirrored the demands of top Iranian officials such as Supreme Leader Ayatollah Ali Khamenei, as well as supporters across the Islamic Republic, who are demanding retaliation against the US for the killing.
Britain has reduced staff at its embassies in Iran and Iraq to a minimum level as a precaution, Sky News understands.
US embassies in France, Algeria, Morocco, and also in some sub-Saharan African nations, have told staff they could be at risk. Sweden has joined the list of countries telling its citizens not to travel to Iraq, outside of the Kurdish region.
Police said millions of people lined the streets of the Iranian capital Tehran as Maj Gen Soleimani's coffin was paraded through the city on Monday.
Ayatollah Ali Khamenei wept during prayers for the general - and the commander's daughter warned that the US and Israel faced a "dark day".
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The outpouring of grief was an unprecedented honour for a man was regarded by many as the second-most powerful person in Iran .
He led the Quds unit of Iran's revolutionary guard and was responsible for expanding the country's influence in the Middle East - mainly through linked Shia militias.
The US blames him for the killing of American troops in Iraq and accused him of plotting new attacks just before his death on Friday.
President Donald Trump ordered last week's strike on the general after the death of an American contractor in Iraq.
Mr Trump has hit back at Iran's vow of "severe revenge" by warning that the US military has identified 52 Iranian sites, including some of cultural significance.