The embassy did not elaborate on the safety risks leading to the “authorised departure”, which allows affected personnel to decide whether to leave.

It falls short of the ordered departure instituted this week for some personnel at the US embassy in Beirut.

The US has built up one of its biggest military deployments in the Middle East as it negotiates with Iran over the Islamic Republic’s nuclear programme.

The latest round of talks ended yesterday with no sign of a breakthrough.

Iran has threatened to strike American bases in the region if it is attacked, and an escalation could also draw in Israel.

The two foes fought a 12-day war in June.

Several countries have begun withdrawing dependents of diplomatic personnel and non-essential staff from some locations in the Middle East, or advising citizens to avoid travel to Iran, amid rising tensions between Washington and Tehran.