(CBS News) Anin the Middle East and other Muslim countries that to close nearly two dozen embassies and consulates over the weekend is "one of the most specific and credible threats I've seen, perhaps since 9/11," House Homeland Security Chairman Mike McCaul, R-Texas, said Sunday on "Face the Nation."
"We're on a high state of alert," McCaul said. "I think the administration's call to close these embassies... was actually very, very smart call - particularly in light of what happened in Benghazi, when warnings were not heeded in that case. I'm glad to see that in this case, they're taking this very seriously."
The threat, signs of which were picked up by U.S. intelligence over the weekend, comes from Al Qaeda of the Arabian Peninsula - also known as AQAP - a terrorist group CBS News correspondent Bob Orr said is "the most active and charged" among al Qaeda.
"The fear is that this may be a big play from a group that has been unable to muster a large-scale attack since 9/11, and they've got some expertise," he said. "They have a bomb maker in Yemen named Ibrahim al-Asiri - he's the guy who built the underwear bombs and printer cartridge bombs. He's a devious genius and we know in the past he's experimented in research trying to build body bombs, that is, implant explosives in human beings which would give a whole new meaning to suicide bombers.
"...While we're not certain at all that's part of this threat," Orr continued, "the fact is he's part of the brain trust there in Yemen that's been working on plots, and it can't be discounted."
McCaul agreed that AQAP is "probably the biggest threat" to U.S. homeland, because it represents a faction of al Qaeda "that still talks about hitting the west and hitting the homeland, and their expertise is chemical explosives, hitting the aviation sector, as we saw with the underwear bomber."
The State Department on Friday, warning of al Qaeda's plans, which may materialize before the end of August, and suggesting that North Africa and the Middle East are the focus of the threat. Set to expire August 31, 2013, the alert urges Americans traveling in that region to be aware of their surroundings: "Terrorists have targeted and attacked subway and rail systems, as well as aviation and maritime service."
Meantime, news of prison breaks in Iraq, Pakistan and Libya that may or may not be linked to al Qaeda suggest the possibility that terrorists are spreading "all throughout the Middle East now - and that presents a very high threat as well," McCaul said. Orr agreed: "This is a lot of manpower for an organization somewhat diminished.
"This week Ayman al-Zawahri, the leader of al Qaeda, had two messages - one earlier in the week saying, 'It's time again to attack the Americans.' And he wanted to free the prisoners in Guantanamo and called for more unrest in Egypt," Orr said. "In the past, when the leader of al Qaeda has come out with public messages, it has sometimes been a 'go' signal for operatives on the ground."
Indeed, there are already operatives in place, CBS News senior correspondent John Miller reports. The problem, Orr said, is while the U.S. government knows "a great deal" about what the terrorist group is trying to do, "we're missing some very important points: the date, the time, the scope of the attack. Intelligence is working overtime this weekend trying to get some of those factors nailed down so we can try to disrupt this plot."
Reporting from in front of the U.S. Embassy in Cairo, Egypt, CBS News foreign correspondent Clarissa Ward saidby the consulate shutdowns. At least one other U.S. non-governmental organization has asked its American employees to stay at home and work from home.
Ward said the "period of concern appears to be these final few days of the Muslim holy month of Ramadan." Why that timing is important, McCaul explained later, is that Ramadan brings their "night of power."
"It's the night that they tried the first attempt on the USS Cole-style attack," McCaul said, also pointing to fifteen years ago this week, when twin U.S. Embassy bombings in Kenya and Tanzania claimed more than 200 lives and injured more than 4,000.
"Zawahiri has basically set out a decree to the jihadists on his website saying, 'Now's the time to attack U.S. interests,'" McCaul said.
The good news, though, McCaul continued, is U.S. agencies has been able to intercept "some loose intelligence on the part of al Qaeda in the Arabian Peninsula - and that's a good thing, if you know that that's happening."
Sen. Chuck Schumer, D-N.Y., later on the program lauded U.S. snooping programs like the National Security Agency's as having been successful, amid raging debate over how to achieve security without sanctioning government overreach.
"I think what today shows is that security is very, very important, and that the agencies in charge are darned good," Schumer said. "They're able to listen in and hear what's going on. They all have disrupted many, many, many terrorist plots and let's hope they're disrupting this one, as well."