The US State Department has told citizens and non-emergency government staff to leave Yemen "immediately" due to security threats.

It comes after the sudden closure of 20 US embassies and consulates on Sunday.

This was prompted by intercepted conversations between two senior al-Qaeda figures, including top leader Ayman al-Zawahiri, US media said.

The US earlier said the closures in North Africa and the Middle East were "out of an abundance of caution".