Iran’s supreme leader threw his support behind the elite Revolutionary Guards in a rare sermon on Friday after their belated admission that they had accidentally downed an airliner triggered days of protests on the streets.

In his first Friday prayers sermon in eight years, Ayatollah Ali Khamenei also told worshippers chanting “Death to America” that the Guards could take their fight beyond Iran’s borders after the US killing of a top Iranian commander.

Washington said any threats would only isolate Iran further.

Washington killed top commander Qassem Soleimani in a drone strike on January 3 and Iran launched missile strikes at US targets in Iraq five days later.

In the tense aftermath, a Ukrainian airliner was shot down by mistake.

“Our enemies... were happy that they found an excuse to undermine the Guards, the armed forces and our system,” Khamenei said in his sermon, heaping praise on the Guards for protecting Iran and renewing a call for US troops to leave the region.

Khamenei said Soleimani’s Quds Force soldiers were “fighters without borders”.

The US department of state’s special representative to Iran, Brian Hook, said in Washington that Iranian threats risked further isolating the country.

But Russia lent Iran some support over the airliner disaster, saying it had been shot down when Tehran was spooked by reports of advanced US stealth fighters in the area.

In his sermon, Khamenei referred to President Donald Trump’s support for those in Iran protesting against the leadership. “These American clowns who lie and say they are with the Iranian people should see who the Iranian people are.”

“The plane crash was a bitter tragedy that burned through our heart,” Khamenei said. “But some tried to use it as an excuse to overshadow the martyrdom of our great commander Soleimani.”