More diplomatic personnel left Iraq on Saturday and Sunday as part of ongoing efforts to "streamline operations", a US official told AFP.

The departures were a continuation of a process that started last week "out of an abundance of caution and due to heightened regional tensions", the official added.

In Lebanon, the US embassy said the State Department on Sunday had ordered staffers' family members and non-emergency US government personnel to leave the country.

A statement on the embassy website cited "the volatile and unpredictable security situation in the region".

Earlier in the day, Washington joined Israel's war against Iran, with US President Donald Trump announcing strikes on the Islamic republic's main nuclear sites.

After the strikes, an adviser to Iran's supreme leader warned that bases in the region used to launch US attacks "will be considered legitimate targets".

Fears were also growing over possible intervention by Iran-backed armed factions around the Middle East, who have threatened Washington's interests should it join Israel's campaign.

Israel has already fought a war in Lebanon with the Tehran-backed militant group Hezbollah, leaving it badly weakened before a ceasefire took hold in November.

On Sunday, Hezbollah said the US strikes revealed "the true face of the United States of America as the largest threat to regional and international security and stability".

The group has not previously expressed any intention to intervene militarily on Iran's side, but its chief Naim Qassem said last week that it would "act as we see fit".

Washington has a "do not travel" advisory in place for Lebanon.

Iraq, meanwhile, has for years navigated a delicate balancing act between its allies Tehran and Washington, has also long been a fertile ground for proxy battles.

On Sunday, the Iraqi government expressed "its deep concern and strong condemnation of the targeting of nuclear facilities" in Iran, spokesperson Basim Alawadi said.

"This military escalation constitutes a grave threat to peace and security in the Middle East and poses serious risks to regional stability," he added.