The United States on Wednesday suspended all commercial passenger and cargo flights between the U.S. and Venezuela, saying the political unrest and tensions there pose a risk to flights.

The announcement by the Department of Homeland Security affected a dwindling number of flights between the two countries, since U.S. airlines no longer fly to Venezuela. The measure reflected the increasingly sour relationship between the Venezuelan government and the U.S., which is leading a campaign to oust President Nicolás Maduro.

Conditions in Venezuela "threaten the safety and security of passengers, aircraft, and crew," the department said. It said the flight suspension will continue indefinitely, though the decision will be reviewed if the situation in Venezuela changes.

American Airlines stopped its flights in mid-March after union leaders told pilots not to go there due to safety concerns. Some other international airlines quit flying to Venezuela years ago because of the country's deteriorating economy.

Some Venezuelan airlines had been operating commercial flights to and from Miami, though those were already affected by the upheaval in the South American country, including after a failed call for a military uprising by the opposition on April 30.

Tuesday's flights between Miami and Caracas on Venezuela's Laser Airlines included a stop in the Dominican Republic, according to the airline.

Also Wednesday, Venezuela's opposition-controlled congress returned to its chamber a day after security forces prevented legislators from entering the National Assembly building for a debate.

Assembly leader Juan Guaidó and other legislators gave speeches denouncing Maduro's government, which has accused them of conspiring with the United States to stage a coup.

The National Assembly has come under increasing pressure from Maduro since the opposition appealed in vain for a military uprising April 30. The assembly's vice president, Edgar Zambrano, was arrested May 8. He is among 14 lawmakers placed under investigation for allegations of treason and other crimes since the failed rebellion.

On Tuesday, police sealed off the National Assembly, purportedly to search for any hidden explosives.

In Washington, the Rev. Jesse Jackson delivered food to American activists who have been occupying the Venezuelan Embassy the past five weeks. Police officers who keep watch around the diplomatic building allowed Jackson to go to the front gate.

The activists, who have ignored trespassing warnings, consider Maduro to be Venezuela's rightful leader. The U.S. and more than 50 other countries contend his presidency is illegitimate and recognize Guaidó as the interim president.

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Associated Press writer Luis Alonso Lugo in Washington contributed to this report.