Updated

The federal government is increasing security measures at some international airports with direct flights to the United States, based on recent intelligence about the continuing, worldwide terror threat, Homeland Security Secretary Jeh Johnson said Wednesday.

Johnson gave no information about a specific threat, saying only that the change was based on the U.S. and its allies “continually (assessing) the global threat environment.”

However, the beefed up security is almost certainly a response to recent intelligence reports suggesting that Al Qaeda-linked terrorists in Syria are working with members of Al Qaeda in the Arabian Peninsula to blow up a commercial aircraft headed to the U.S. or Europe, as reported first by ABC News.

A counterterrorism official told AP that the terrorists are attempting to create a bomb that would go undetected through airport security.

The official declined to describe the kind of information that triggered this warning. Officials in the past have raised concerns about non-metallic explosives being surgically implanted inside a traveler's body, designed to be undetectable in pat-downs or metal detectors.

Americans and others from the West have traveled to Syria over the past year to join al Nusra Front's fight against the Syrian government. The fear is that fighters with a U.S. or Western passport -- and therefore subject to less stringent security screening -- could carry such a bomb onto an American plane.

Al Qaeda's affiliate in Yemen, called Al Qaeda in the Arabian Peninsula, long has been fixated on bringing down airplanes with hidden explosives. It was behind failed and thwarted plots involving suicide bombers with explosives designed to hide inside underwear and explosives hidden inside printer cartridges shipped on cargo planes.

The call for increased security was not connected to Iraq or the recent violence there, said a second U.S. counterterrorism official who was not authorized to speak publicly by name. Another U.S. official, also speaking on condition of anonymity, said the increased security measures had nothing to do with the upcoming July Fourth holiday or any specific threat.

The extra security is out of an "abundance of caution," the U.S. official said.

Johnson has directed the Transportation Security Administration to carry out the changes.

“We will work to ensure these necessary steps pose as few disruptions to travelers as possible,” he said. “Aviation security includes a number of measures, both seen and unseen, informed by an evolving environment.”

Meanwhile, the State Department has instructed U.S. Embassy employees in Algeria to avoid U.S.-owned or operated hotels through July 4 and the Algerian Independence Day on July 5.

"As of June 2014 an unspecified terrorist group may have been considering attacks in Algiers, possibly in the vicinity of a U.S.-branded hotel," according to the message from the U.S. Embassy in Algeria.

State Department spokeswoman Jen Psaki did not provide details about the reasons for the increased security.

"I would say broadly speaking that the threat of foreign fighters is a concern that we share with many counterparts in the world, whether that's European or others in the Western world, where we've seen an increase in foreign fighters who have traveled to Syria and other countries in the region and returning," Psaki said. "And so we have been discussing a range of steps we can take in a coordinated fashion for some time."

Southwest Airlines, which along with subsidiary AirTran Airways, flies between the U.S. and Mexico and the Caribbean, doesn't expect the directive to have much impact on its operations, spokesman Chris Mainz said. He said the focus likely would be in other parts of the world, although the airline's security personnel have been contacted by the Homeland Security Department. Mainz declined to comment on those discussions.

American Airlines spokesman Joshua Freed said the company has been in contact with Homeland Security about the new requirements but declined to comment further.

The United Kingdom also said it is increasing security measures “in conjunction with international partners and the aviation industry.” Officials also said they don’t anticipate significant disruptions for passengers and that they will not raise the terror-threat level.

The Associated Press contributed to this report