Iran's Supreme Leader Ayatollah Ali Khamenei reiterated on Wednesday a promise to retaliate against Israel over the killings of Iranian generals in Syria.

Khamenei spoke at a prayer ceremony celebrating the end of the Muslim holy month of Ramadan, saying the airstrike that demolished Iran's consulate in Syria earlier this month was “wrongdoing" against a diplomatic post that is considered Iranian territory.

“When they attack our consulate section it looked like they attack on our territory,” Khamenei said.

“The evil regime must be punished, and it will be punished.”

The strike killed 12 people: seven Iranian Revolutionary Guard members, four Syrians and a Hezbollah militia member.

Israel has not acknowledged its involvement, though it has been bracing for an Iranian response to the attack that was a significant escalation in their long-running shadow war.

State TV broadcast Khamenei's remarks live. He did not elaborate on the way Iran would retaliate.

Khamenei also criticised the West, particularly the US and Britain, for supporting Israel in its war against Hamas in Gaza.

“It was expected they (would) prevent (Israel) in this disaster. They did not. They did not fulfil their duties, the Western governments,” he said.

Iran supports anti-Israeli militant groups like Palestinian Hamas and Lebanese Hezbollah. It does not recognize Israel.