Day was just breaking on Saturday in Tehran when a crowd of faithful called for "revenge" in front of the coffin of Ali Khamenei, displayed for a public farewell to the face of the Islamic Republic.

Iranian state television announced at around 06:00 (02:30 GMT) the start of the national funeral of the late supreme leader in a vast complex which includes a mosque.

"We are not here for a funeral but for revenge," cries a eulogist in front of weeping worshippers.

In the crowd, many waved red flags with the inscription "Martyr" or the yellow flags of the Lebanese Hezbollah, a movement supported by Tehran.

Ali Khamenei was killed on February 28 at the age of 86, when his residence in Tehran was bombed by Israeli-American strikes that ignited the Middle East.

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Among the worshippers were many people of conservative appearance: women in chadors and men dressed in black. Some came with their families and children.

"I never had the chance to see the supreme leader up close and I regret it. Today I came to say a final goodbye," Javad Akbari, 43, a food worker, told AFP.

Two rows of Iranian flags surround Khamenei's coffin, which is displayed under the dome of the immense Mosalla, designed for prayers.

The walls of the site are covered with large portraits of Ayatollah Khamenei, at different periods of his life, including when he accompanied soldiers on the front during the devastating war against Iraq (1980-1988).

"We promised the supreme leader that we would stay with him until the end. All these people are here for him" because he "sacrificed himself for us," says Reza, a 37-year-old university professor.

- Fortified camp -

Religious and patriotic songs add to the emotion, while worshippers pray on the ground.

As is the tradition in Shiite Islam, many beat their chests as a sign of mourning.

Some chant "Death to America, death to Israel!", a slogan regularly heard at official rallies.

Water is intermittently sprayed on the crowd as temperatures are expected to exceed 35°C during the day.

Many faithful hold portraits of Mojtaba Khamenei, who succeeded his father as supreme leader.

Since his appointment in March, the leader has still not appeared in public and only speaks through statements attributed to him.

These public funerals are taking place against the backdrop of a fragile ceasefire with the United States and six months after major protests against the high cost of living and the government.

Central Tehran on Saturday resembled a fortified camp: concrete blocks and police cars blocked all streets leading to the site for about two kilometers.

Iranian authorities say they expect between 15 and 20 million participants in Tehran alone for this national tribute which takes place over six days with a stopover in neighboring Iraq.

On Monday, Ali Khamenei's body will be carried through the streets of Tehran for a final farewell, before the funeral procession travels the following day to the holy city of Qom. He will be buried on July 9 in the holy city of Mashhad (northeast Iran), his birthplace.