SITE via AFP - Getty Images; IntelCenter via AP From left: al Qaeda's chief Ayman al-Zawahiri and Nasser al-Wahishi, leader of al Qaeda in the Arabian Peninsula.

An intercepted electronic communication in which two of al Qaeda’s top world leaders agreed they “wanted to do something big” this past Sunday is what caused the U.S. government to shut nearly two dozen diplomatic posts around the world, according to intelligence sources.

Ayman al-Zawahiri, Osama bin Laden’s successor as the head of al Qaeda, and Nasir al-Wahishi, leader of al Qaeda in the Arabian Peninsula, wanted to time a significant attack to a Muslim holiday known as Laylat al-Qadr, the 27th night of Ramadan and the day the Koran was revealed to Mohammed. This year the holiday, also known as the “Night of Destiny" or the "Night of Power,” fell on the weekend of August 3 and 4.

The communications did not give the specific target or the method of attack, but multiple U.S. law enforcement and intelligence sources told NBC News there was no known domestic component. The most likely country targeted was thought to be Yemen, where al Qaeda does have the resources to pull off a significant operation.

Wahishi has become an increasingly significant player in al Qaeda’s global leadership. NBC analyst Evan Kohlmann said there have been reports that Zawahiri may have officially appointed al-Wahishi his number two, making him deputy commander of the terror group.

A third major al Qaeda leader was also party to the communications, and expressed the desire to blow himself up in an attack, something he had not been allowed to do in the past.

The State Department has extended the closure of nearly a dozen embassies in North Africa and the Middle East through the weekend and perhaps longer because of the possibility of attack. Several other European countries, including France and Great Britain, also closed diplomatic posts in the region.

“There's a high level of confidence in the sources of the information,” Rep. Adam Schiff, D.-Calif., a senior member of the House Intelligence Committee, told MSNBC’s Chuck Todd Monday. “We get chatter all the time ... But to take this kind of a broad action, to shut down this many embassies over this broad terrain, to have multiple briefings to the President ... that demonstrates a high level of confidence that this threat is real."

Officials said that the original intercept was corroborated by a second source, which was also non-specific. Multiple officials said that if the intelligence community had picked up this “chatter” from lower level people, it wouldn’t have sparked nearly this kind of reaction.

But on Monday U.S. officials still said there was little new in the way of specifics about the possible operation, including the type of weapon that would be used. Asked if there was even confirmation that the target is U.S. or Western, one senior counterterrorism official said, “There’s nothing.”

Officials said the widely reported claim that an al Qaeda team is in place is “conjecture,” and is probably based on analysis of how far in advance such a team would have begun moving. One U.S. intelligence official said he believes other agencies are mixing up what is broadly known about AQAP’s capabilities and methodology with this current threat stream.

Despite reports, there is also no hard information that al Qaeda in the Arabian Peninsula plans to use an "implanted" bomb, as it has attempted to do in the past. AQAP's senior bomb maker, Ibrahim Hassan al-Asiri, has designed several implant bombs in the past, but thus far there is no indication he's involved in this threat.

In 2009, al-Asiri designed a bomb that his brother carried in his rectum in an attempt to assassinate Prince Mohammed Bin Nayef, Saudi Arabia's terror chief. The bomber died but the prince suffered only minor burns.

AQAP has become the most sophisticated of the many Al Qaeda affiliates. Operating mainly out of Yemen, it has attempted to carry out high-profile attacks on the U.S. and its interests overseas. AQAP dispatched the so-called “underwear bomber,” Umar Farouk Abdulmutallab, who tried to detonate a bomb in an airplane over Detroit on Christmas Day 2009, and the terror group also launched a foiled plot to destroy U.S. cargo planes using a cartridge bomb.

Earlier this year, U.S. and British intelligence uncovered a new aviation plot utilizing a more sophisticated underwear bomb, which the British recovered.

Just last week, the U.S. launched a series of attacks on AQAP -- three Predator strikes in five days -- but did not kill any of the group's top leadership. Also last week, President Obama met at the White House with Yemen's new president, Abdrabuh Mansur Hadi, to discuss counter-terrorism efforts.

Jim Miklaszewski, Andrea Mitchell and Pete Williams contributed reporting to this story.

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