The official reason for why the Federal Aviation Administration abruptly closed the airspace over El Paso, Texas, for about eight hours early Wednesday remains unclear as Congress questions the explanation given by the Trump administration.

The restriction was initially set to last 10 days, but it was quickly lifted by the FAA. Transportation Secretary Sean Duffy attributed the airspace closure to an alleged Mexican “cartel drone incursion,” which he said was “neutralized” Wednesday morning.