Countries around the world voiced fears of a Middle East conflagration after the United States and Israel launched strikes on Iran Saturday, and Iran targeted US bases in the region in retaliation.

- Iran Guards vow 'severe' punishment -

Iran's Revolutionary Guards vowed to punish the "murderers" of supreme leader Ali Khamenei, after his death was confirmed by state television.

"The hand of revenge of the Iranian nation for a severe, decisive and regrettable punishment for the murderers of the Imam of the Ummah will not let go of them," the Guards said in a statement.

Launching a major attack alongside Israel against Iran, US President Donald Trump is openly pursuing the goal he once adamantly rejected -- regime change.

Trump, who ordered a military buildup in the Middle East unseen since the 2003 invasion of Iraq, made clear in a video address that the goal of the bombing campaign dubbed "Epic Fury" was to topple the cleric-run state that has long been a US nemesis.

Lebanese Prime Minister Nawaf Salam said Saturday that his country refused to be dragged into war, after Israel and the United States launched strikes against Iran.

Authorities fear the Iran-backed Lebanese militant group Hezbollah could become involved in the conflict, which saw the US and Israel bomb Iran on Saturday and Tehran respond with missile attacks.

Just before the operation began, Israel announced it was carrying out strikes on Hezbollah infrastructure in south Lebanon.

BEIRUT, Feb 28 (Reuters) - Lebanese Prime Minister Nawaf Salam on Saturday said he would not accept anyone dragging "the country into adventures that threaten its security and unity", in an indirect message to the Iran-backed Lebanese armed group Hezbollah.

In a statement released after Israel and the United States launched strikes on Iran, Salam noted the "serious developments" in the region and called on "all Lebanese to act with wisdom and patriotism, placing Lebanon and the Lebanese people’s interests above any other consideration".

Ayatollah Ali Khamenei, Iran's supreme leader since 1989 and sworn enemy of the West, was killed in the opening salvo of a massive US and Israeli attack, sparking a new wave of retaliatory missile strikes from Tehran on Sunday.

Iranian state television confirmed Khamenei's death early Sunday, hours after President Donald Trump announced the killing of the 86-year-old cleric he described as "one of the most evil people in History".

By Jasper Ward

WASHINGTON, Feb 28 (Reuters) - U.S. President Donald Trump said on Saturday that the United States had begun "major combat operations" in Iran, warning that there may be U.S. casualties.

The strikes, which Trump said were aimed at destroying Iranian missiles and annihilating its navy, follow repeated U.S.-Israeli warnings that they would strike Iran again if it pressed ahead with its nuclear and ballistic missile programs.

"I do not make this statement lightly. The Iranian regime seeks to kill," Trump said in a video shared on Truth Social.

US President Donald Trump announced a major attack against Iran on Saturday, vowing to "annihilate" the country's navy and missile sites, and urging Iranians to overthrow their government.

In a video address after the United States and Israel started bombing Iran, Trump made clear the goal was destruction of the Islamic republic's military and toppling of the authorities in power since the 1979 revolution.

By Phil Stewart, Parisa Hafezi and Menna AlaaElDin

WASHINGTON, DUBAI, CAIRO, Feb 28 - Israel launched a pre-emptive attack against Iran on Saturday, and a United States attack is underway, plunging the Middle East into a renewed military confrontation and further dimming hopes for a diplomatic solution to Tehran's nuclear dispute with the West.

Feb 28 (Reuters) - The Israeli operation against Iran on Saturday was coordinated with the U.S., an Israeli defence official told Reuters.

The operation was planned for months and the launch date was decided weeks ago, the official added.

(Reporting by Rami Ayyub; Editing by Kate Mayberry)

Feb 28 (Reuters) - Israel said it launched a pre-emptive attack against Iran on Saturday, pushing the Middle East into a renewed military confrontation and further dimming hopes for a diplomatic solution to Tehran's long-running nuclear dispute with the West.

The New York Times, citing a U.S. official, reported that U.S. strikes on Iran were underway. A source told Reuters that Iran's supreme leader, Ayatollah Ali Khamenei, was not in Tehran and had been transferred to a secure location.