Eighteen of the 19 US diplomatic missions recently closed due to security threats will reopen on Sunday.
The state department says its embassy in the Yemeni capital Sanaa will stay closed “because of ongoing concerns”.
The US closed 19 diplomatic missions in the Middle East and Africa last Sunday in response to what it said was a threat of a terrorist attack.
The consulate in the Pakistani city of Lahore, which closed after a separate threat, will also not reopen yet.
“We will continue to evaluate the threats to Sanaa and Lahore and make subsequent decisions about the reopening of those facilities based on that information,” said spokeswoman Jen Psaki.
“We will also continue to evaluate information about these and all of our posts and to take appropriate steps to best protect the safety of our personnel, American citizens travelling overseas, and visitors to our facilities.”
On Thursday, at least 14 suspected al-Qaeda militants – reportedly including seven from Saudi Arabia – were killed in Yemen in three drone strikes, Yemeni officials said.
The number of US strikes in Yemen has been stepped up over the past month.
Eighteen of the 19 US diplomatic missions recently closed due to security threats will reopen on Sunday
Yemen is a stronghold of al-Qaeda in the Arabian Peninsula (AQAP) – an al-Qaeda offshoot considered by Washington to be the most dangerous to the West.
The US statement said the Sanaa embassy would stay closed because of concerns about a “threat stream” emanating from AQAP, without providing further details.
Most US employees at the Sanaa embassy were ordered to leave the country on Tuesday.
The embassy closures, along with a US global travel alert, came after the US reportedly intercepted al-Qaeda messages.
Reports said they were between senior figures talking about a plot against an embassy.
The US closed its consulate in Lahore on Thursday and evacuated all non-essential staff following what it described as “a credible threat”.
US officials said the evacuation was undertaken as a precaution and not related to the closure of the other diplomatic missions.
Thursday’s drone attacks in Yemen targeted a group of suspected militants, killing four of them in Wadi al-Jadd in the southern province of Hadramout, said Yemeni officials.
A day earlier, Yemen said it had foiled a major al-Qaeda plot against oil pipelines and ports.
Two strikes in Marib and Hadramout provinces killed 10 suspected militants, the security officials said, while another seven people died in a drone attack on Wednesday.
While the US has acknowledged targeting militants in Yemen with drones, it does not comment publicly on its policy or the raids.
About 30 suspected militants have been killed in a series of such raids in Yemen since 28 July, news agencies report.
A global travel alert has been issued by the US state department because of fears of an unspecified al-Qaeda attack.
The department said the potential for an attack was particularly strong in the Middle East and North Africa.
The US intercepted electronic communications between senior al-Qaeda figures, according to officials quoted by the New York Times.
The alert comes shortly after the US announced nearly two dozen embassies and consulates would be shut on Sunday.
The US state department said the alert expires on August 31, 2013, and it recommended US citizens travelling abroad be vigilant.
“Current information suggests that al-Qaeda and affiliated organizations continue to plan terrorist attacks both in the region and beyond, and that they may focus efforts to conduct attacks in the period between now and the end of August,” the statement said.
The alert warned of “the potential for terrorists to attack public transportation systems and other tourist infrastructure”.
In its report, the New York Times says high-level intercepts were collected and analyzed this week and that the CIA, state department and White House immediately recognized their significance.
President Barack Obama has ordered that “all appropriate steps” be taken to protect Americans in response to a threat of an al-Qaeda attack, AFP news agency quoted a White House official as saying.
A global travel alert has been issued by the US state department because of fears of an unspecified al-Qaeda attack
“The president is being updated on a potential threat occurring in or emanating from the Arabian Peninsula,” the official added.
Nancy Pelosi, the Democratic leader in the House of Representatives, said that congressional leaders had been briefed about the alert.
“There is some understanding of the seriousness of the threat,” she told reporters.
Republican lawmaker Jason Chaffetz said he understood there was “a very real worldwide threat”.
Dutch Ruppersberger, the top Democrat on the House intelligence committee, said the threat was not prompted by “the regular chit chat” gleaned from would-be militants online or elsewhere.
“The most important thing we have to do is protect American lives,” he told the Associated Press news agency.
An unnamed senior US official told NBCthe threat may be related to the Islamic holy month of Ramadan, which ends next week.
In the Muslim world, Sunday is a work day. In other parts of the world US diplomatic offices are shut on Sunday.
The official said the state department had “been apprised of information” leading it to take these “precautionary steps… out of an abundance of caution”.
Last year on September 11, the US consulate in Benghazi, Libya, was attacked, leaving four Americans dead.
Other embassies are routinely targets of protesters.
The US diplomatic missions to be closed on Sunday are in Abu Dhabi, United Arab Emirates; Algiers, Algeria; Amman, Jordan; Baghdad, Iraq; Cairo, Egypt; Dhahran, Saudi Arabia; Djibouti, Djibouti; Dhaka, Bangladesh; Doha, Qatar; Dubai, United Arab Emirates; Erbil, Iraq; Jeddah, Saudi Arabia; Kabul, Afghanistan; Khartoum, Sudan; Kuwait City, Kuwait; Manama, Bahrain; Muscat, Oman; Nouakchott, Mauritania; Riyadh, Saudi Arabia; Sanaa, Yemen and Tripoli, Libya.