Shoe bomb alert! The U.S. government has released a warning to airlines to pay close attention to shoes as there is a higher chance of terrorists attempting to hide explosives in their shoes, according to new intelligence information.

Recent intelligence from the United States and other countries has indicated that terrorists are working on new shoe-bomb designs. However officials made it clear that there is no specific threat or known plan at this time, CNN reports.

The information caused the Department of Homeland Security to warn airlines to pay particular attention to possible explosives hidden in shoes on flights from other countries to the United States. Some officials said that the warning is being released as a precaution.

"This threat is not specific or credible enough to require a specific response. DHS often issues these alerts out of an abundance of caution, but this does not necessarily rise to the level of facilitating a response," a intelligence official said according to CNN.

Some officials said that the possibility is so low that they don't even know why DHS released a warning. Yet some said the warning should be expanded to include cosmetics and liquids in addition to shoes. An official said that this threat isn't connected to warnings earlier this month about toothpaste and cosmetics being used to hide explosives on flights to Russia for the Olympics.

Shoe bombs are a reality. In 2001, just two months after the 9/11 terrorist attacks, passengers on an American Airlines flight from Paris to Miami stopped British citizen Richard Reid from setting off explosives in his sneakers.
On Christmas Day in 2009,  a man tried to blow up an overseas flight to Detroit by carrying explosives in his underwear.

Under current TSA policy, all passengers must remove their shoes when going through security checkpoints. With the warning, passengers may notice additional searches, including swabs to detect explosives.

The warning includes 20 to 30 cities overseas. Among the list are Johannesburg, Paris, London and Cairo, as well as some cities in the Middle East.