The Department of Homeland Security told airlines Wednesday there’s a potential shoe-bomb threat for overseas flights into the United States, NBC News reported.

Several officials familiar with the warning told NBC News that “very recent intelligence” believed to be credible noted potential plans to attack passenger jets with explosives hidden in shoes.

Image source: AP/Erik S. Lesser

Image source: AP/Erik S. Lesser 

Therefore, officials said, airlines will be playing close attention to passenger shoes on flights into the U.S. from overseas departure points, which could mean heightened passenger screenings and pat-downs.

The bulletin to airlines instructs screeners to use explosive trace detection swabs when checking shoes passengers are wearing, as well as those in carry-on luggage.

No specific airline, country, time, or plot scenario was named in the threats, officials said, adding that it’s unrelated to the Winter Olympics in Sochi, Russia.

“It’s a reminder that we are under constant threat and an advisory to airlines be on their A game,” another official familiar with the threat intelligence told NBC News.

More from NBC News:

British national Richard Reid — the “Shoe Bomber” — first raised the specter of such threats just three months after the Sept. 11, 2001 terror attacks when he attempted to ignite bombs hidden in his sneakers on a Paris-to-Miami flight.

Reid was subdued by passengers and crew. He pleaded guilty to terrorism charges in 2002 and is now serving a life sentence at a maximum security federal prison in Florence, Colo.

Since the botched attack, federal security officials have screened the shoes of most airline passengers at security checkpoints.