ERBIL, Kurdistan Region of Iraq - US President Donald Trump on Sunday issued a video address discussing the progress of combat operations against Iran, urging the Iranian people to "take back your country" and calling on security forces to lay down their arms in exchange for immunity.

The president's remarks come as the conflict, which began with joint US-Israeli "preemptive" strikes on Iran and has since involved numerous regional actors as Tehran strikes US military bases in the Middle East, enters its third day.

"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. America is with you," Trump said in the address. "The rest will be up to you, but we'll be there to help."

Washington has voiced its hopes that the latest offensive will see the toppling of the Iranian government, with longtime Supreme Leader Ayatollah Ali Khamenei, ostensibly the public face of the Islamic Republic, being killed in his compound in an airstrike on Friday.

Trump also claimed that "the entire [Iranian] military command is gone as well, and many of them want to surrender... they want immunity — they're calling by their thousands."

"I once again urge the Revolutionary Guard [IRGC], the Iranian military, and police to lay down your arms and receive full immunity or face certain death. It will be certain death. It won't be pretty," he continued.

Also on Sunday night, British Prime Minister Keir Starmer announced that US forces will be allowed to conduct operations from UK military bases in the region, marking a shift from a stance against such practice beforehand that drew the ire of Trump.

"We are not joining these strikes, but we will continue with our defense operations in the region," Starmer said in a video message, referencing British jets intercepting Iranian missiles over allied nations.

"We all remember the mistakes of Iraq, and we have learned those lessons. We were not involved in the initial strikes on Iran, and we will not join offensive action now." 

Iran’s security chief Ali Larijani said Sunday that the US and Israel have "set the heart of the Iranian nation ablaze" after Khamenei was killed, vowing that Tehran will strike its enemies "with a force never seen before."

On the same day, the US military announced that three service members had been killed and five others were seriously wounded during the conflict.