Washington: United States President Donald Trump announced that Iran's Supreme Leader, Ayatollah Seyyed Ali Khamenei, had been killed in a U.S.-Israeli military strike, marking a dramatic escalation in hostilities in the Middle East.

In a Truth Social post, Donald Trump wrote that Khamenei was 'one of the most evil people in history,' and framed the killing as retribution for Americans and others harmed by Iran's leadership.

'This is not only Justice for the people of Iran,' Trump wrote, 'but for all Great Americans, and those people from many Countries throughout the World, that have been killed or mutilated by Khamenei and his gang of bloodthirsty THUGS.

Trump added that Khamenei's killing offered 'the single greatest chance for the Iranian people to take back their Country.'

Khamenei, who ruled Iran's religious autocracy for more than three decades, is believed to have been killed in a strike in his compound in the capital, Tehran. The 86-year-old's death was confirmed by the state-run IRNA news agency, which did not elaborate on a cause.

His assassination followed years of tensions with successive U.S. and Israeli governments over Iran's nuclear program, and his refusal to give up his country's right to develop nuclear energy.

It came just weeks after his security forces brutally crushed widespread protests that first broke out across the country over rampant inflation, but spiralled into broader demonstrations against Khamenei and the Islamic regime that has ruled Iran since 1979.