The United States on Thursday restricted movements of its diplomats in Israel over security fears, the embassy said, as concerns mount of Iranian retaliation over an Israeli strike.

"Out of an abundance of caution, US government employees and their family members are restricted from personal travel" outside the Tel Aviv, Jerusalem and Beersheeva areas "until further notice," an embassy notice said.

"The security environment remains complex and can change quickly depending on the political situation and recent events," it said.

The US embassy did not state the cause for new alarm, which comes more than six months into Israel's war with Hamas.

But Iran has vowed retaliation after Israel on April 1 destroyed an Iranian diplomatic building in Damascus, killing seven members of the clerical state's elite Revolutionary Guards including two generals.

Israel has warned of retaliation to any strike against it.

The United States has vowed that its security support for Israel is "ironclad" and Secretary of State Antony Blinken has reached out to counterparts from China and other countries to encourage them to use their influence to urge Iran not to "escalate."