State Department spokeswoman Jen Psaki said the decision to keep the embassies and consulates closed is "not an indication of a new threat."
She said the continued closures are "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."
Diplomatic facilities will remain closed in Egypt, Jordan, Libya, Yemen, Saudi Arabia and Kuwait, among other countries, through Saturday, Aug. 10. The State Department announcement Sunday added closures of four African sites, in Madagascar, Burundi, Rwanda and Mauritius.
The U.S. has also decided to reopen some posts on Monday, including those in Kabul, Afghanistan, and Baghdad.
The Obama administration announced Friday that the posts would be closed over the weekend and the State Department announced a global travel alert, warning that al-Qaida or its allies might target either U.S. government or private American interests.
The weekend closure of nearly two dozen U.S. diplomatic posts resulted from the gravest terrorist threat seen in years, the top Republican on the Senate Intelligence Committee said Sunday.
Sen. Saxby Chambliss said "the chatter" intercepted by U.S. intelligence agencies led the Obama administration to shutter the embassies and consulates and issue a global travel warning to Americans.
"Chatter means conversation among terrorists about the planning that's going on - very reminiscent of what we saw pre-9/11," Chambliss, R-Ga., told NBC's "Meet the Press."
"This is the most serious threat that I've seen in the last several years," he said.
Rep. C.A. Dutch Ruppersberger of Maryland, the top Democrat on the House Intelligence Committee, told ABC's "This Week" that the threat intercepted from "high-level people in al-Qaida in the Arabian Peninsula" was about a "major attack."
Yemen is home to al-Qaida's most dangerous affiliate, blamed for several notable terrorist plots on the United States. They include the foiled Christmas Day 2009 effort to bomb an airliner over Detroit and the explosives-laden parcels intercepted the following year aboard cargo flights.
Rep. Peter King, who leads the House Homeland Security subcommittee on counterterrorism and intelligence, said the threat included dates but not locations of possible attacks.
"The threat was specific as to how enormous it was going to be and also that certain dates were given," King, R-N.Y., said on ABC.
Rep. Adam Schiff, a House Intelligence Committee member, said the "breadth" of the closures suggests U.S. authorities are concerned about a potential repeat of last year's riots and attacks at multiple embassies, including the deadly assault in Benghazi, Libya, where the U.S. ambassador and three other Americans were killed.
In addition, Interpol, the French-based international policy agency, has issued a global security alert in connection with suspected al-Qaida involvement in several recent prison escapes including those in Iraq, Libya and Pakistan.
Those prison breaks add to the concerns about an attack, said Schiff, D-Calif., also noting the approaching end of the Islamic holy month of Ramadan.
"So you have a lot things coming together. ... But all of that would not be enough without having some particularly specific information," he said.
The Obama administration's decision to close the embassies and the lawmakers' general discussion about the threats come at a sensitive time as the government tries to defend recently disclosed surveillance programs that have stirred deep privacy concerns and raised the potential of the first serious retrenchment in terrorism-fighting efforts since Sept. 11.
The Senate Judiciary Committee chairman has scoffed at the assertion by the head of the National Security Agency that government methods used to collect telephone and email data have helped foil 54 terror plots.
Schiff said he has seen no evidence linking the latest warnings to that agency's collection of "vast amounts of domestic data."
Other lawmakers defended the administration's response and promoted the work of the NSA in unearthing the intelligence that lead to the security warnings.
"The bottom line is ... that the NSA's job is to do foreign intelligence," Ruppersburger said. "The whole purpose is to collect information to protect us."
Added King, a frequent critic of President Barack Obama, "Whether or not there was any controversy over the NSA at all, all these actions would have been taken."
Friday's warning from the State Department urged American travelers to take extra precautions overseas, citing potential dangers involved with public transportation systems and other prime sites for tourists. It noted that previous terrorist attacks have centered on subway and rail networks as well as airplanes and boats. It suggested travelers sign up for State Department alerts and register with U.S. consulates in the countries they visit. The alert expires Aug. 31.
The statement said al-Qaida or its allies might target either U.S. government or private American interests.
Associated Press writer Michele Salcedo contributed to this report.