An army trooper on patrol Monday in Sana, Yemen. American officials said that it was highly unusual for senior Qaeda leaders in Pakistan to discuss operational matters with its affiliates.
The Obama administration’s decision last week to close nearly two dozen diplomatic missions and issue a worldwide travel alert came after the United States intercepted electronic communications in which the head of Al Qaeda ordered the leader of the group’s affiliate in Yemen to carry out an attack as early as this past Sunday, according to American officials.
The intercepted conversations last week between Ayman al-Zawahri, who succeeded Osama bin Laden as the head of the global terrorist group, and Nasser al-Wuhayshi, the head of the Yemen-based Al Qaeda in the Arabian Peninsula, revealed what American intelligence officials and lawmakers have described as one of the most serious plots against American and Western interests since the attacks on Sept. 11, 2001.
American officials said that it was highly unusual for senior Qaeda leaders in Pakistan to discuss operational matters with the group’s affiliates. The communication between the two men seems to indicate that Mr. Zawahri — whom administration officials have portrayed as greatly diminished and hindered in running a global terror network while deep in hiding — still has a strong influence over a group in Yemen that has become Al Qaeda’s most powerful offshoot.
In recent weeks, counterterrorism officials said, Mr. Zawahri has elevated Mr. Wuhayshi to what one official described as the new “general manager” of the global terror network, making him the second most important man in the organization.
The identities of the two Qaeda leaders whose discussions were monitored and the imminent nature of the suspected plot — in the intercepts, the terrorists mentioned Sunday as the day that the attacks were to take place — help explain why the United States, as well as other Western governments, took such extraordinary steps in the past few days to close embassies and consulates in the Middle East and North Africa.
“This was significant because it was the big guys talking, and talking about very specific timing for an attack or attacks,” said one American official who had been briefed on the intelligence reports in recent days.
Yemen experts said that Mr. Wuhayshi, who was Bin Laden’s private secretary in Afghanistan, remains particularly loyal to the core group of Qaeda operatives who are believed to mostly be hiding in Pakistan.
“Wuhayshi was groomed by Osama bin Laden to take on a leadership role, and he was able to use his connections to Bin Laden to become head of AQAP,” said Gregory D. Johnsen, a Yemen scholar at Princeton and author of “The Last Refuge,” a book about Al Qaeda in Yemen.
Mr. Wuhayshi fled to Iran from Afghanistan in 2001, but was extradited to Yemen in 2003. In 2006, he was part of a mass breakout from a prison in Sana that led to a resurgence of Al Qaeda’s operations in Yemen. In recent years, the Qaeda group there, Al Qaeda in the Arabian Peninsula, has tried to carry out several high-profile attacks.
One was an attempt to blow up a trans-Atlantic jet over Detroit on Dec. 25, 2009, using explosives sewn into a passenger’s underwear. Last spring, a C.I.A. double agent spirited out of Yemen an even more sophisticated explosive that was meant to blow up an American commercial airliner.
A campaign of American drone strikes and a Yemeni Army offensive have put the Qaeda affiliate under heavy pressure over the past 18 months, with militants pushed out of the territory they had been holding and back into hiding.
But even with these setbacks and the years of drone strikes, the group has continued to publish an English-language online magazine, Inspire. Yemen has been at the center of the recent uptick in threat levels, and Mr. Johnsen said American estimates of the group’s followers had actually increased.
“The question I have is, If the Obama administration is confident that its strategy in Yemen is correct, then why is Al Qaeda growing in Yemen and why is the group still capable of forcing the United States to shut down embassies in more than a dozen countries?” Mr. Johnsen said.
In an article posted on the Web on Friday and published on Saturday, The New York Times agreed to withhold the identities of the Qaeda leaders whose conversations were intercepted after senior American intelligence officials said the information could jeopardize their operations. The names were disclosed Sunday by McClatchy Newspapers, and after the government became aware of the article on Monday, it dropped its objections to The Times’s publishing the same information.
The State Department on Monday defended its decision on Sunday to extend the closing of 19 diplomatic posts in the Middle East and North Africa through at least Saturday because of continued fears of an imminent attack.
“We are going to keep evaluating information as it comes in, keep analyzing the various intelligence that we’re getting in in regards to this stream,” said a State Department spokeswoman, Marie Harf. “Over all, what we are doing is taking precautionary steps out of an abundance of caution to protect our people and our facilities and visitors to those facilities overseas.”
The embassies that will be closed include the ones in Yemen, Libya, Egypt, Saudi Arabia and the United Arab Emirates, the statement said.
Embassies in Algiers, Baghdad and Kabul reopened on Monday, as did the United States Embassy in Pakistan, even though the Qaeda threat that shuttered many other diplomatic missions emanated in part from that country. Still, rumors of an impending militant attack on Islamabad, the capital — and not necessarily on an American target — coursed through diplomatic and security circles last weekend.
One Western diplomat, speaking on the condition of anonymity, said his mission had received reports that militant attackers had congregated in the Margalla Hills, which overlook the city. But the diplomat stressed that those reports were unconfirmed, and that while the security situation in the city had tightened, there was little information to suggest an impending assault.
Britain and France said Monday that they had extended the closing of their embassies in Yemen until at least Thursday, after Washington announced that its embassy would stay shut until after Ramadan ends, which is to occur around Thursday in most places. The German mission was still closed Monday, while Norway had shut its embassies in Yemen and Saudi Arabia.
Counterterrorism analysts, as well as former intelligence official, said closing the embassies — and depriving Al Qaeda of targets, at least for now — may have deterred an attack.
“The announcement itself may also be designed to interrupt Al Qaeda planning, to put them off stride,” Michael V. Hayden, a former C.I.A. director, said on “Fox News Sunday.” “To put them on the back foot, to let them know that we’re alert and that we’re on at least to a portion of this plotline.”