The intercepted message last week between Zawahri and Nasser al-Wuhayshi, the head of the Yemen-based Al Qaeda in the Arabian Peninsula, revealed one of the most serious plots against American and Western interests since the attacks on September 11, 2001, the New York Times reported.
"Zawahiri ordered the leader of Al Qaeda's affiliate in Yemen to carry out an attack as early as this past Sunday," the paper quoted American officials as saying.
The conversations of the top al-Qaeda leaders and the imminent nature of the suspected plot "help explain why the US, 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," it said.
The US closed 22 missions across the Middle East on Sunday and extended the closures of 19 of them till August 10.
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"This was significant because it was the big guys talking, and talking about very specific timing for an attack or attacks," an American official, who had been briefed on the intelligence reports in recent days, was quoted as saying.
In recent weeks, Zawahri has elevated 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 organisation, the paper said.
The American officials also said that it was highly unusual for senior al-Qaeda leaders in Pakistan to discuss operational matters with the group's affiliates.
Last week, in a 15-minute audio message posted online, Zawahiri had accused the US of orchestrating former Egyptian President Mohamed Morsi's ouster.