Tens of thousands of Iranians thronged Tehran's vast outdoor prayer complex Saturday to view the coffin of Ayatollah Ali Khamenei, who ruled the Islamic Republic for 37 years before being killed on the war's opening day. Dressed in black and draped in the red, white and green flags of the Islamic Republic, mourners held up posters and printed sheets bearing images of Khamenei and his son and successor, Mojtaba Khamenei. The casket, along with those of several family members killed in the same February 28 airstrike, was brought to an outdoor stage for public viewing after a day of indoor lying-in-state for senior Iranian leaders and foreign officials. Crowds filled the courtyard of the Imam Khomeini Grand Mosalla, beating their chests, wailing and waving the banners of the Islamic Republic and historic Shi'ite martyrs. "Let us wail!" a compere urged over loudspeakers. "Everybody chant oppressed, everyone say Hussein" — invoking Shi'ite traditions of sacrifice tied to the Prophet Muhammad's grandson, killed at Karbala. The Israeli strike that killed Khamenei also killed his daughter, a grandchild, his daughter-in-law and son-in-law, according to Iranian state media. Their five flag-draped caskets, placed on a raised platform, included a tiny one for a 14-month-old granddaughter. Iran's military and security institutions vowed revenge, and chants of "Death to America" echoed through the Mosalla, state broadcaster Seda va Sima reported. A country marked by war The funeral comes at a critical moment for Iran, where clerical rulers backed by the Revolutionary Guards feel emboldened by having survived what they viewed as an existential war against their most powerful adversaries. But beneath the appearance of unity and devotion, public support for the Islamic Republic has worn thin, analysts say. Mojtaba Khamenei, long close to the Guards' elite, has not appeared in any new image since being wounded in the strike that killed his father. Thousands of U.S. and Israeli strikes hit military, energy and civilian targets during weeks of war that began with Khamenei's killing on February 28, killing more than 3,000 people in Iran according to state media. Iran retaliated with strikes on U.S. bases, missiles fired at Israel and attacks on energy targets in Gulf Arab states, choking oil shipping through the Strait of Hormuz. At least 13 U.S. troops have been killed. Thousands more have died across the region, notably in Lebanon, where Israel continues fighting Hezbollah and where strikes have flattened vast civilian areas in the south. The U.S. and Iran reached a shaky ceasefire by early April and signed an initial agreement in June, though sporadic attacks continue. Observers say the war, which killed many senior Iranian military and security officials, has empowered hardline leaders more willing than Khamenei himself to launch direct attacks against adversaries. Shi'ite martyrdom In Iran's theocratic system, Khamenei was not only head of state and leader of a revolutionary movement but the earthly representative of Shi'ite Islam's 12th imam, who disappeared in the ninth century. His death at enemy hands feeds into a powerful Shi'ite tradition of martyrdom and mourning. The casket was unveiled Thursday night and lay in state Friday in the great prayer hall built to honor Khamenei's predecessor, Ayatollah Ruhollah Khomeini. It will remain at the Mosalla until Sunday evening. Islamic tradition calls for burial within a day of death, but the risks of holding a mass funeral during wartime forced authorities to postpone the ceremony until after last month's truce. Seven days of ceremonies After what authorities are billing as a massive procession through central Tehran on Monday, the remains will move to Qom, the seminary city and center of Iran's Shi'ite hierarchy, for Tuesday's ceremonies. Wednesday's rites will take place in the Iraqi shrine cities of Najaf and Karbala, drawing prominent figures from Iran's regional network of Shi'ite allies. Burial is set for Thursday, after another procession, in Mashhad near the tomb of Imam Reza — a deeply revered figure in Iran and Khamenei's own birthplace, where he was born in 1939. Authorities plan to mobilize millions over the coming days, offering transport, food and lodging to encourage turnout from Iran's population of more than 90 million.