Hundreds of thousands of Iranians have turned out in the capital, Tehran, for the funeral of former President Akbar Hashemi Rafsanjani.
Supreme Leader Ayatollah Ali Khamenei will lead prayers at the ceremony.
Rafsanjani, president from 1989 to 1997, died of a heart attack on Sunday at the age of 82.
He was one of the most influential figures since Iran's 1979 revolution, criticised for harsh rule but later a key supporter of reformists.
Three days of official mourning began on Monday.
The funeral is expected to see a significant presence of reformists and hardliners, with whom Rafsanjani lost favour in the latter years of his political life.
The former president will be buried next to Iranian revolutionary leader Ayatollah Khomeini.
2011 file photo of former Iranian president Akbar Hashemi Rafsanjani

Mr Rafsanjani was a key supporter of President Hassan Rouhani and had backed Iran's landmark deal with world powers over its nuclear programme.
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Death a bitter blow for reformists
President Rouhani was reportedly at Rafsanjani's hospital bedside in Tehran on Sunday where doctors had fought to save him.
"Islam lost a valuable treasure, Iran an outstanding general, the Islamic revolution a courageous flag-bearer and the Islamic system a rare sage," Mr Rouhani later said.
Iran's Supreme Leader Ayatollah Ali Khamenei, a Muslim cleric, is leading prayers at the ceremony

Iran's Supreme Leader Ayatollah Ali Khamenei, a Muslim cleric, is leading prayers at the ceremony
Mourners gather round coffin of Akbar Hashemi Rafsanjani during a mourning ceremony at Jamaran mosque in
On Monday, mourners visited a Tehran mosque to touch Rafsanjani's coffin
Tributes and condolences have come from around the world, though many Iranians have taken to social media critical of Rafsanjani's repression of human rights.
The US State Department described Rafsanjani as a "prominent figure" in Iranian history.
Rafsanjani's youngest son Yaser, 46, thanked those mourning his father for their "loyalty and kindness".
He told state TV: "I see scenes of affection that I cannot believe. People's prayers for our father console our hearts."
Grey line
Goodbye to a major figure, by Lyse Doucet, BBC Chief International Correspondent
This is the most significant funeral in Iran since the country's revolutionary leader Ayatollah Khomeini was buried in 1989.
Akbar Hashemi Rafsanjani was one of the last major figures of the 1979 revolution.
In its early years, he was known for his harsh rule. But over the decades, the wily politician who held almost every major position in government became known for his pragmatic approach to Iran's theocracy.
He pushed for a greater rapprochement with the West and more social and economic freedoms.
His credentials gave him the courage and the clout to speak out. The reformists he backed, including the current President Hassan Rouhani, have now lost a key ally in their incessant struggle for power against the hardliners.