A a member of the US Senate Intelligence Committee says the al-Qaeda threat that has closed 21 US embassies and consulates in the Middle East is the most serious in years.
The State Department on Friday issued a worldwide travel alert warning that al-Qaeda may be planning attacks this month, particularly in the Middle East and North Africa.
Senator Saxby Chambliss (Republican) said the "chatter" (electronically monitored communication) among suspected terrorists is reminiscent of what preceded the September 11 attacks in 2001.
"There is an awful lot of chatter out there," he said on Meet the Press on NBC TV, adding it was "very reminiscent of what we saw pre-9/11."
Senator Chambliss said a National Security Agency surveillance programme that electronically collects communications on cellphones and emails (known as intercepts) helped gather intelligence about this threat.
Those programmes "allow us to have the ability to gather this chatter," he said. "If we did not have these programs then we simply wouldn't be able to listen in on the bad guys."
"This is the most serious threat that I've seen in the last several years," Senator Chambliss said.
Senator Lindsey Graham (Republican) said on CNN that the actions taken to close the embassies and issue the global travel alert showed that the Obama administration had learned lessons from last year's attacks on the US mission in Benghazi, when an ambassador and three other Americans were killed.
"Benghazi was a complete failure. The threats were real there. The reporting was real. And we basically dropped the ball. We've learned from Benghazi, thank God, and the administration is doing this right," he said.
The US State Department reportedly believes that a major plot is under way and that the team to carry it out has been selected and is in place.
However, neither the date or the target of the planned attack are known.
The ABC reports the State Department has extended the closures of embassies and consulates until 10 August. They have been closed since Sunday.
The department said the extension was due to caution.