Intercepted communications between al Qaeda leaders were part of the reason for the closure of US embassies in the Middle East and Africa. US media said chatter at the highest level had raised fears of a major attack.
Officials were reported as saying late on Monday that the closures were triggered by the intercept of secret messages between al Qaeda chief Ayman al-Zawahri and his deputy in Yemen.
The New York Times reported that electronic communications between al-Zawahri, who replaced Osama bin Laden as head of al Qaeda, and Nasser al-Wahishi, the head of the Yemen-based al Qaeda in the Arabian Peninsula (AQAP) had featured in the decision to close the embassies.
"This was significant because it was the big guys talking, and talking about very specific timing for an attack or attacks," the newspaper quoted one official as saying.
US officials were also quoted as telling the AP news agency that a message from the al Qaeda leader to al-Wahishi had figured highly in the administration's reasoning.
An abundance of caution
However, in a press briefing on Monday, White House spokesman Jay Carney declined to comment on specific intelligence behind the actions.
"We believe that this threat is significant, and we are taking it seriously for that reason and have taken the actions that the State Department announced out of an abundance of caution," said Carney.
While Carney did say that the threat emanated from the Arabian Peninsula, he added that it could be directed elsewhere. "We cannot be more specific," he said.
State Department spokeswoman Maria Harf added that there would have been closure in any case, because of religious holidays.
"I would also remind people that many of these posts would have been closed for much of the week because of the Eid holiday so we're just extending those closures for the week," said Harf.
A statement released by US State Department spokesperson Jen Psaki on Sunday said embassies in 19 countries in the Muslim world would remain closed through August 10 after closures over the weekend. Among the US diplomatic missions to remain closed this week are those in Yemen, Egypt, Jordan, Libya, Saudi Arabia, and Kuwait.
Senate Intelligence Committee, Republican Senator Saxby Chambliss told the US broadcaster NBC that the information received revealed "the most serious threat that I've seen in the last several years."
European nations - which also shut the doors of their diplomatic missions - extended their closures into the week as well.
While the German Foreign Ministry said there was still "no concrete evidence of concrete threats," the German embassy in the Yemeni capital, Sana'a, was closed for an extra day on Monday.
The French Foreign Minister Laurent Fabius said the Sana'a embassy would stay closed on Tuesday and Wednesday, while the British Foreign Office said its Yemen embassy would be shut until the end of the Eid al-Fitr festival on Thursday - the end of the holy month of Ramadan.
rc/jm (AP, dpa, Reuters)