US security chiefs have met to review the chances of a terrorist attack after they received intelligence leading to the closure of 21 American embassies and consulates across the Muslim world.
President Barack Obama was briefed following the meeting, according to the White House.
"The President has received frequent briefings over the last week on all aspects of the potential threat and our preparedness measures," a spokesperson said this morning.
Meanwhile in the UK The Foreign Office is continuing to urge Britons to leave Yemen as a two-day closure of its embassy in the capital Sana'a begins.
Among those present at last night's meeting were the secretaries of state, defence and homeland security as well as the directors of the FBI, CIA and the National Security Agency. General Martin Dempsey, chairman of the Joint Chiefs of Staff was also in attendance.
In addition to embassy closures, a global travel warning to US citizens was issued, following fears that al-Qa'ida or its allies might target US government buildings or private American interests.
The US State Department said the potential for terrorism was particularly acute in the Middle East and North Africa, with a possible attack coming from the Arabian Peninsula.
US officials have pointed specifically to Yemen, the home of al-Qa'ida in the Arabian Peninsula, seen as the organisation's most dangerous affiliate. The group is blamed for several notable plots against the US, from the attempted Detroit bombing on Christmas Day 2009 to the explosives-laden parcels intercepted the following year aboard cargo flights.
The warnings come after the US intercepted electronic communications between senior al-Qa'ida figures.
The diplomatic facilities affected stretch from the north-west African country of Mauritania to Afghanistan.
The alert, which expires on 31 August, comes less than a year since the fatal attack last September on a US diplomatic building in the Libyan city of Benghazi.