All flights to and from Texas’ El Paso International Airport, which borders Mexico, have been halted for “special security reasons,” the U.S. Federal Aviation Administration said.

The El Paso airport confirmed the development in an Instagram post, saying all flights to and from the airport were grounded.

The FAA did not specify the nature of the “security reasons.” It said the temporary restrictions would be in place until February 21.

Aviation observers note that a flight restriction of this length and scale — closing an international airport and surrounding airspace — is very unusual outside of major security events.

The FAA’s “national defense airspace” designation implies involvement of the Department of Defense or other national security agencies, although no official confirmation on that has been made publicly available yet.