US embassies in the Middle East are to remain closed for the rest of the week as supporters of the National Security Agency's sweeping surveillance powers used the unspecified terror alert to bolster the case against reining in the controversial measures.

The closures follow the alleged interception of al-Qaida communications in Yemen, which intelligence committee members in Congress have been told were collected overseas using powers granted to the NSA under the Foreign Intelligence Surveillance Act – not the bulk surveillance programs disclosed by the Guardian and the Washington Post thanks to whistleblower Edward Snowden.

A privacy group questioned the publicity given to the latest alert after the State Department announced on Sunday evening that the number of embassies and consulates closed "out of an abundance of caution"

would be increased, with some remaining shut for up to a week.

Rebublican senator Saxby Chambliss said the NSA had identified threats that were the most serious for years and akin to levels of "terrorist chatter" picked up before 9/11.

"These [NSA] programs are controversial, we understand that," he told NBC's Meet the Press on Sunday. "But they are also very important … If we did not have these programs, then we simply would not be able to listen in on the bad guys."

Senator Lindsey Graham added: "To the members of Congress who want to reform the NSA program, great. If you want to gut it, you make us much less safe, and you're putting our nation at risk. We need to have policies in place that can deal with the threats that exist, and they are real, and they are growing."

Most warnings about NSA over-reach have focused on its domestic bulk surveillance program authorised under section 215 of the Patriot Act. Yet several news organizations reported on Monday that the information justifying the latest alert came from an intercepted communication between al-Qaida leader Ayman Zawahiri and the chief of the terrorist organization's Yemeni affiliate. Such information would have been collected overseas using powers granted to the NSA under section 702 of the Foreign Intelligence Surveillance Act.

Critics of the NSA surveillance programs pointed out that the latest threat had nothing to do with the bulk collection of domestic phone data. Senator Ron Wyden, the Oregon Democract who has been a longstanding voice against the bulk collection of phone records, said the latest threat was "serious".

But Wyden, a member of the Senate intelligence committee, added: "While I can't go into specific details, the vice chairman of the Senate intelligence committee noted yesterday that this information was collected using section 702 of the Foreign Intelligence Surveillance Act, rather than the Patriot Act. I still haven't seen any evidence that the NSA's dragnet surveillance of Americans' phone records is providing any unique value to American counterterrorism efforts."

Privacy campaigners criticised the widespread linking of the latest terror alerts with the debate over the domestic powers of the NSA. Amie Stepanovich, a lawyer with the Electronic Privacy Information Center, said: "The NSA's choice to publish these threats at this time perpetuates a culture of fear and unquestioning deference to surveillance in the United States."

News of the fresh terror alert came as Congress looked increasingly likely to pursue fresh attempts to limit the NSA's domestic powers when it returns in September.

"The NSA takes in threat information every day. You have to ask, why now? What makes this information different?" added Stepanovich.

"Too much of what we hear from the government about surveillance is either speculation or sweeping assertions that lack corroboration. The question isn't if these programs used by this NSA can find legitimate threats, it's if the same threats couldn't be discovered in a less invasive manner. This situation fails to justify the NSA's unchecked access to our personal information."

Late on Sunday, the State Department confirmed the closures would continue for several days.

"Given that a number of our embassies and consulates were going to be closed in accordance with local custom and practice for the bulk of the week for the Eid celebration at the end of Ramadan, and out of an abundance of caution, we've decided to extend the closure of several embassies and consulates including a small number of additional posts," the department said in a statement.

"This is not an indication of a new threat stream, merely an indication of our commitment to exercise caution and take appropriate steps to protect our employees including local employees and visitors to our facilities."

Posts in Abu Dhabi, Amman, Cairo, Riyadh, Dhahran, Jeddah, Doha, Dubai, Kuwait, Manama, Muscat, Sanaa, Tripoli, Antanarivo, Bujumbura, Djibouti, Khartoum, Kigali, and Port Louis are instructed to close for normal operations from Monday, August 5 through to Saturday, August 10.

Other posts that are normally open on Sunday, but were closed on Sunday, August 4, were due to reopen for normal operations on August 5, including: Dhaka, Algiers, Nouakchott, Kabul, Herat, Mazar el Sharif, Baghdad, Basrah, and Erbil.