The US State Department has issued a global travel alert because of fears of an unspecified al-Qaeda attack.
The department, which said the potential for an attack was particularly strong in the Middle East and North Africa, intercepted communications between senior al-Qaeda figures, according to reports
It was also revealed that nearly two dozen embassies and consulates would close on Sunday.
US citizens travelling abroad are being advised to be vigilant until the alert expires on 31 August 2013.
“Current information suggests that al-Qaeda and affiliated organisations continue to plan terrorist attacks both in the region and beyond, and that they may focus efforts to conduct attacks in the period between now and the end of August,” a statement said.
The British embassy in Yemen is to be closed on Sunday and Monday, according to the UK Foreign Office.