Biden vows 'ironclad' support for Israel against any Iranian retaliation

US President Joe Biden has promised "ironclad" support for Israel as Iran threatens reprisals over a strike that levelled an Iranian consulate building in the Syrian capital, Damascus and killed two generals.

Biden's promise comes on Wednesday despite his public criticism of Prime Minister Benjamin Netanyahu over the toll on civilians in Israel's brutal war in besieged Gaza, especially after a strike killed seven aid workers.

Iran is "threatening to launch a significant attack on Israel," Biden told a news conference.

"As I told Prime Minister Netanyahu, our commitment to Israel's security against these threats from Iran and its proxies is ironclad," Biden said.

"Let me say it again — ironclad. We're going to do all we can to protect Israel's security," said Biden, who was speaking next to Japanese Prime Minister Fumio Kishida.

US officials have voiced alarm over the prospect of an imminent strike against Israeli interests after Israel on April 1 destroyed the consulate building, killing seven members of Iran's Revolutionary Guard including two generals.

Israel 'must be punished'

Iran's Supreme Leader Ali Khamenei warned in a speech on Wednesday that the "evil regime" of Israel "must be punished and will be punished."

"When they attack the consulate, it is as if they have attacked our soil," he said.

Israeli Foreign Minister Israel Katz reposted, in a Persian-language statement on social media site X, "If Iran attacks from its territory, Israel will respond and attack Iran."

The United States since the start of the war has sought to prevent it from spreading including to Lebanon, where Iran supports Hezbollah.

The United States has been tightlipped in its public reaction to the April 1 strike, saying it has not determined whether Israel struck a diplomatic facility, which would violate international agreements on the inviolability of embassies and consulates.