About one-third the U.S. diplomatic posts that were temporarily shuttered due to a "serious threat" of al Qaeda attack reopened on Monday, hours after officials extended closures at 15 others through Saturday and shut four more.
Nine embassies and consulates opened their doors again, but a further 19 would be closed through Saturday “out of an abundance of caution,” the State Department said.
“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,” the State Department said in a statement late Sunday.
They added that many would have been shut for the celebration of Eid at the end of Ramadan.
"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 State Department added.
The countries with closure orders covered much of the Muslim and Arab world.
However, U.S. posts in Dhaka, Algiers, Nouakchott, Kabul, Herat, Mazar el Sharif, Baghdad, Basrah and Erbil reopened on Monday.
Missions in Abu Dhabi, Amman, Cairo, Riyadh, Dhahran, Jeddah, Doha, Dubai, Kuwait, Manama, Muscat, Sanaa, Tripoli, Antananarivo, Bujumbura, Djibouti, Khartoum, Kigali, and Port Louis will be closed until at least Saturday.
Officials told NBC News that the threat appears to be linked to Yemen, but the State Department has only confirmed that the warnings are generally tied to al Qaeda.
Yemen is home to perhaps the most dangerous terror network affiliate, known as al Qaeda in the Arabian Peninsula (AQAP). The lethal wing is considered responsible for several terrorist strikes on the United States, including the foiled Christmas Day 2009 attempt to bomb an airplane over Detroit.
“The one thing we can talk about is the fact that there’s been an awful lot of chatter out there,” Sen. Saxby Chambliss (R.-Ga.), the ranking member of the Senate Intelligence Committee, said Sunday on NBC’s “Meet the Press.” He added that the chatter is “very reminiscent of what we saw pre-9/11.”
“This is the most serious threat that I’ve seen in the last several years,” he added.
The Obama administration announced the weekend closures on Friday, and the State Department later released a global travel warning.
The alert called on American travelers to take additional precautions overseas, pointing to potential dangers involved with public transportation systems and other likely locations for tourists. It said that previous terrorist attacks have targeted subway and rail networks as well as airplanes and boats.
The alert is slated to expire Aug. 31.
The decision to close the U.S. diplomatic missions on Sunday — a work day in most of the region — came almost a year after an attack on a U.S. diplomatic post in Benghazi, Libya, that killed the ambassador and three other Americans.
NBC News' Catherine Chomiak and the Associated Press contributed to this report.