The U.S. Department of Homeland Security (DHS) suspended air travel with Venezuela, citing conditions that “threaten the safety and security of passengers, aircraft, and crew.”

Secretary of State Mike Pompeo approved the order to suspend all commercial passenger and cargo flights and Secretary of Transportation Elaine Chao implemented it, DHS reported.

“This determination is based on the ongoing political instability and increased tensions in Venezuela and associated inadvertent risk to flight operations,” the Homeland Security statement explained.

The flight suspension will remain in effect indefinitely until Secretaries Pompeo and Chao decide to revise the order to reflect improved conditions in Venezuela.

Several carriers have already voluntarily suspended service to Venezuela, notably including American Airlines this March and United and Delta in 2017. A protest from the American Airlines pilots’ union, which feared for the safety of its members, halted that airline’s services.

Other airlines cited political upheaval and/or the deteriorating economy under dictator Nicolás Maduro, which could make takeoffs and landings unsafe. Local media have reported on violent clashes near Venezuela’s airports.

Reuters reported concerns the flight suspension will harm the starving population by making it more difficult for family members abroad and humanitarian organizations to send them food, medicine, and supplies. Amnesty International compared the flight suspension to a “collective blockade” of Venezuela because U.S.-based cargo companies have been the most affordable way to deliver humanitarian aid.

“This will be a catastrophe for a lot of people. This will complicate enormously the transportation of humanitarian aid to the country,” Feliciano Reyna of nonprofit medical aid organization Accion Solidaria told the New York Times.

The Times anticipated the flight suspension will most heavily impact Avior Airlines, the largest private service in Venezuela, which has been running daily flights to Miami from Caracas and Puerto La Cruz.

Maduro denounced the flight ban on Wednesday as an “inhuman” action taken by the United States out of “frustration and spite.”

“They prohibit Venezuelan registered airplanes to go to the United States and the Americans to come to our country, as if Venezuela were Mars,” he said.