The US government has urged all Americans to leave Lebanon immediately, following a similar warning for those in Iraq.

The US embassy in Beirut warned that the security situation in Lebanon was "volatile and unpredictable", with air strikes, drone activity and rocket attacks reported, particularly in the south, the Beqaa Valley, and parts of the capital.

US universities in the region have also been threatened, the embassy warned, adding that Iran and its aligned militias may target institutions in Lebanon.

The advisory follows recent developments, including a US fighter jet reportedly being shot down over Iran and strikes by the Israel Defense Forces (IDF) on parts of Beirut.

On Friday, the embassy in Beirut recommended that Americans should not travel to Lebanon and that those already in the country must depart while commercial flights remain available.

Those opting to stay were advised to prepare contingency plans for emergency situations and to be ready to shelter in place if the situation worsened.

The embassy also "strongly" urged Americans in southern Lebanon, near the Syrian border, in refugee settlements and in the  southern suburbs of Beirut, including Dahieh, to leave  those areas immediately.

Earlier this year, in February, the US government had ordered all non-essential staff to leave its embassy in Beirut following a security review.

About 50 members of US embassy staff were ordered to leave at the time.

Americans in Iraq were also urged to evacuate on Thursday, days after a US journalist was kidnapped in Baghdad by an Iran-backed militia group.

The US embassy in Iraq said that militia groups aligned with Iran may conduct attacks in central Baghdad in the coming 24 to 48 hours.

On Friday, the IDF confirmed it had launched another wave of strikes on Tehran and had begun targeting parts of Beirut.

Meanwhile, an explosion "inside a UN position" in Lebanon injured three UN peacekeepers, the United Nations Interim Force in Lebanon (Unifil) said on Friday.

Two of the peacekeepers were seriously injured, the agency said.

Spokeswoman Kandice Ardiel said the blast occurred near El Adeisse, in southern Lebanon, with the origin of the explosion not yet identified.