Six airlines cancelled flights to Venezuela on Saturday, an industry group said, after the U.S. aviation regulator warned of dangers from "heightened military activity" amid a major buildup of American forces in the region.

Spain's Iberia, Portugal's TAP, Chile's LATAM, Colombia's Avianca, Brazil's GOL, and Trinidad and Tobago's Caribbean have suspended their flights to the country, said Marisela de Loaiza, president of the Venezuelan Airlines Association (ALAV).

She did not specify how long the flight suspensions would last.

Panama's Copa Airlines, Spain's Air Europa and PlusUltra, Turkish Airlines, and Venezuela's LASER are continuing to operate flights for now.

The U.S. Federal Aviation Administration on Friday urged civilian aircraft in Venezuelan airspace to "exercise caution" due to the "worsening security situation and heightened military activity in or around Venezuela."

"Threats could pose a potential risk to aircraft at all altitudes, including during overflight, the arrival and departure phases of flight, and/or airports and aircraft on the ground," it said.

Washington has sent an aircraft carrier strike group, other Navy warships as well as stealth aircraft to the region – deployments it says are aimed at curbing drug trafficking but which have sparked fears in Caracas that regime change is the goal.

A U.S. terrorism designation takes effect Monday for a drug cartel allegedly headed by leftist Venezuelan leader Nicolas Maduro – a move that some believe could presage military action against his government.

Washington's forces have carried out strikes against more than 20 alleged drug-smuggling vessels in the Caribbean Sea and eastern Pacific Ocean since early September, killing more than 80 people.

But the United States has yet to release concrete evidence that the vessels it targeted were used to smuggle drugs or posed a threat to the country, and regional tensions have flared as a result of the campaign and the accompanying military buildup.