Palm Beach, Florida - President Donald Trump on Sunday warned Iran's security forces to surrender or be killed, after the US military said it destroyed the headquarters of the elite Revolutionary Guards

"I once again urge the Revolutionary Guard, the Iranian military, and police to lay down your arms and receive full immunity or face certain death," Trump said in a video address.

"It will be certain death. It won't be pretty."

Elsewhere in the six-minute address, Trump vowed that Washington would "avenge" the deaths of three US service members as he acknowledged that more casualties were likely in the conflict that has already killed at least 200 Iranians.

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"Sadly, there will likely be more before it ends," he said. "But America will avenge their deaths and deliver the most punishing blow to the terrorists who have waged war against, basically, civilization."

He further urged the people of Iran to rise up to topple the Islamic Republic after Supreme Leader Ayatollah Ali Khamenei was killed in the opening salvo of the US-Israeli bombardment.

"I call upon all Iranian patriots who yearn for freedom to seize this moment to be brave, be bold, be heroic, and take back your country," he said. "America is with you."