WASHINGTON » American spies and intelligence analysts today scoured email, phone calls and radio communications between al-Qaida operatives in Yemen and the organization’s senior leaders to determine the timing and targets of a potentially spectacular attack that officials said they came across in monitoring militants’ "chatter."

Lawmakers have said it was a massive plot in the final stages, but they offered no specifics. Intelligence officials told The Associated Press that the target could be a single embassy or a number of posts, or still other Western objectives. The diffuse nature of the monitored information 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 today, including well-defended embassies in Kabul, Afghanistan, and Baghdad.

Officials wouldn’t say who intercepted the initial suspect communications — the CIA, the National Security Agency, the Defense 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. The official spoke on condition of anonymity because the official was not authorized to discuss the spying publicly.

Once the plot was detected however, NSA analysts could use the programs that leaker Edward Snowden revealed to determine whom the plotters may have contacted around the world. Snowden revealed one program that collected telephone data such as the numbers called and the duration of calls on U.S. telephone networks. Another program searched global Internet usage. Therefore, if a new name was detected in the initial chatter, the name or phone number of that person could be run through the NSA databases to see whom he called or what websites or emails he visited.

The surveillance is part of the continuing effort to track the spread of al-Qaida from its birthplace in Afghanistan and Pakistan to countries where governments and security forces are weaker and less welcoming to the U.S. or harder for American counterterrorist forces to penetrate — such as Syria, Iraq, Somalia, Mali and Libya — as well as Yemen, already home to al-Qaida’s most dangerous affiliate, Al-Qaida in the Arabian Peninsula. Administration officials have said the plot seems to be centered in and may be carried out by that affiliate, known as AQAP.

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-Qaida in Yemen. Last week, Yemeni President Abed Rabbo Mansour Hadi met with President Barack Obama at the White House. Administration officials would not say if the threat was discussed in that meeting.

"Clearly, AQAP is the most active terrorist organization there and has been the most operationally active affiliate of al-Qaida core," State Department spokeswoman Marie Harf said.

The Yemeni government also went on high alert today, stepping up security at government facilities and checkpoints, according to a Mideast diplomat in the U.S. The diplomat said the Yemen alert was related to the threat that led to the temporary shutdown of the U.S. embassies.

White House spokesman Jay Carney wouldn’t say whether the threat extends to the United States or whether Americans should be fearful because of the alerts.

"What we know is the threat emanates from, and may be focused on, occurring in the Arabian Peninsula," Carney said. "It could potentially be beyond that, or elsewhere."

"We cannot be more specific," he said.

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-Qaida in the Islamic Maghreb, in neighboring Mali.

The model for both is the U.S. operation in Somalia. CIA officers there provide intelligence, and special operators advise U.N. 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-Qaida’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.

"There isn’t much known about the where, so they are trying to gauge their reaction as widely as possible," Rep. Adam Schiff, D-Calif., said today. "The locus of the highest concern is in the area of the (Arabian) Peninsula and emanates from there," said Schiff, who is a member of the House intelligence committee. "Given al-Qaida in the Arabian Peninsula’s past focus on airlines," Schiff said Americans should be vigilant about airline travel and mass transportation.