The U.S. Federal Aviation Administration has told American airlines to be cautious while flying to Saudi Arabia and crossing the skies of the country.

According to Reuters, the agency cited ongoing military activities and disruption to navigation systems as reasons for the warning on Sunday. In the agency’s aviation notice, it said the threats could endanger aircraft at all altitudes, when crossing the skies, and during landing and takeoff.

The notice is valid until 19 Azar and also applies to operators of aircraft registered in the United States.

The warning was issued after attacks on Saturday and Sunday on Riyadh’s international airport. In the Saturday attack, 13 people were killed and more than 300 were injured.