The Department of Homeland Security issued a bulletin Wednesday warning airlines of possible attempts to attack passenger jets using explosives packed in shoes, Fox News reports. The threat is described as being unrelated to the Sochi Olympics.

The intelligence was not specific to an airline or time frame, but it suggested flights from overseas, not domestic flights within the U.S., are potentially at risk. The DHS bulletin calls on screeners at overseas airports to increase their use of explosive detection swabs on passengers’ shoes, and passengers flying into the U.S. can expect more pat-downs.