An intercepted secret message between al-Qaeda chief Ayman al-Zawahri and his deputy in Yemen about plans for a major terror attack was the trigger that set off the current shutdown of many U.S. embassies, two officials told The Associated Press on Monday.

A U.S. intelligence official and a Mideast diplomat said al-Zawahri's message was picked up several weeks ago and appeared to initially target Yemeni interests. The threat was expanded to include American or other Western sites abroad, officials said, indicating the target could be a single embassy, a number of posts or some other site. Lawmakers have said it was a massive plot in the final stages, but they have offered no specifics.

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Ayman al-Zawahri took over as al-Qaeda's leader after the death of Osama bin Laden. (Hamid Mir/Reuters)

The intelligence official said the message was sent to Nasser al-Wahishi, the head of the terror network's organization, based in Yemen, known as al-Qaeda in the Arabian Peninsula.

Both officials spoke on condition of anonymity because they were not authorized to discuss the sensitive issue publicly.

American spies and intelligence analysts on Monday scoured email, phone calls and radio communications between al-Qaeda operatives in Yemen and the organization's senior leaders to determine the timing and targets of the planned attack.

The call from al-Zawahri, who took over for Osama bin Laden after U.S. Navy SEALs killed the al-Qaeda leader in May 2011, led the Obama administration to close diplomatic posts from Mauritania on Africa's west coast through the Middle East to Bangladesh, east of India, and as far south as Madagascar.

The U.S. did decide to reopen some posts on Monday, including well-defended embassies in Kabul, Afghanistan, and Baghdad.

The Yemeni government also went on high alert Monday, stepping up security at government facilities and checkpoints.

NSA involvement?

Officials in the U.S. wouldn't say who intercepted the initial suspect communications — the CIA, the National Security Agency, the Defence Intelligence Agency or one of the other intelligence agencies — that kicked off the sweeping pre-emptive closure of U.S. facilities. But an intelligence official said the controversial NSA programs that gather data on American phone calls or track Internet communications with suspected terrorists played no part in detecting the initial tip. That official spoke on condition of anonymity because the official was not authorized to discuss the spying publicly.

U.S. embassies shut through Aug. 10

  • Abu Dhabi, United Arab Emirates.
  • Amman, Jordan.
  • Cairo, Egypt.
  • Riyadh, Saudi Arabia.
  • Dhahran, Saudi Arabia.
  • Jeddah, Saudi Arabia.
  • Doha, Qatar.
  • Dubai, United Arab Emirates.
  • Kuwait City, Kuwait.
  • Manama, Bahrain.
  • Muscat, Oman.
  • Sana'a, Yemen.
  • Tripoli, Libya.
  • Antananarivo, Madagascar.
  • Bujumbura, Burundi.
  • Djibouti, Republic of Djibouti.
  • Khartoum, Sudan.
  • Kigali, Rwanda.
  • Port Louis, Mauritius.

A U.S. official familiar with the threat information said the decision to close the embassies was based on a broad swath of information, not just the intercept. The official said the U.S. has made clear in the past that AQAP makes its own operational decisions — that there are back-and-forth communications between al-Qaeda leadership and AQAP, but that they operate independently.

AQAP also has been blamed for the foiled Christmas Day 2009 effort to bomb an airliner over Detroit and the explosives-laden parcels intercepted the following year aboard cargo flights. The CIA and Pentagon jointly run drone targeting of al-Qaeda in Yemen.

The Obama administration announced the embassy closures one day after President Barack Obama met with Yemeni President Abdo Rabby Mansour Hadi. A person familiar with the meeting said Obama and Hadi did discuss al-Qaeda in the Arabian Peninsula but their talks did not directly result in the embassy closures and travel ban.

That person insisted on anonymity because the person was not authorized to discuss the private meeting.

19 diplomatic posts closed

The U.S. also has stepped up surveillance in Africa, flying unarmed observation drones from Libya, focused in that country on a mix of militant groups in the town of Darna. A newer U.S. operation opened last year at an airfield in Niger, aimed at tracking another affiliate, al-Qaeda in the Islamic Maghreb, in neighbouring Mali.

The model for both is the U.S. operation in Somalia. CIA officers there provide intelligence, and special operators advise UN peacekeeping troops on tactics as well as delivering surveillance and intelligence — carrying out the occasional raid against pirates or militants.

Acting on what it said was an "overabundance of caution," the State Department on Sunday closed a total of 19 diplomatic posts until next Saturday. They include posts in Bangladesh and across North Africa and the Middle East as well as East Africa, including Madagascar, Burundi, Rwanda and Mauritius. The closure of the African facilities came just days before the 15th anniversary of al-Qaeda's bombings of American diplomatic missions in Kenya and Tanzania.

Those two embassies targeted in the Aug. 7, 1998 attacks were rebuilt as more heavily fortified structures away from populated areas where they would be less vulnerable to attack.

One senior U.S. diplomat in the region said his diplomatic facility was keeping a skeleton U.S. staff working to provide some U.S. citizen services, but was limiting movements in and out of the area and remained closed to the general public. Diplomatic staff were taking precautions standard for the region even in normal times — avoiding areas of known militant activity and varying times and routes for business or personal meetings. The official spoke on condition of anonymity because the official was not authorized to discuss the closures publicly.

The British and German embassies in Yemen also were closed. Norway's Foreign Ministry, too, restricted public access to 15 of its embassies in the Middle East and Africa, including its post in Saudi Arabia.