HAVANA - A United Airlines jetliner carrying 135 passengers from Washington to a Mexican beach resort made an unplanned landing in Cuba on Sunday after a strange odor was detected on board.

United Airlines Flight 831 left Dulles airport in the morning and was bound for Cancun but instead diverted to Havana around noon after "the crew noticed an unfamiliar smell in the cabin," airline spokesman Charles Hobart said in a statement.

"In an abundance of caution, the pilots decided to land the aircraft at the nearest available airport," he said. "The plane landed routinely and safely in Havana and we are working to re-accommodate our customers."

Gloria Berbena, a spokeswoman for the US Interests Section, which Washington maintains in Havana instead of an embassy since the two nations do not have full diplomatic relations, said a second plane arrived from the United States later Sunday and flew out with the passengers.

Berbena did not know whether they continued to Cancun or returned to the United States, or whether the original aircraft was still in Cuba. US diplomats on the island were in close contact with their Cuban counterparts on the matter, she said.

Cuban airport and government officials contacted by The Associated Press had no immediate comment.

"We have nothing to inform," said an operator who answered the phone at the airport.

No United aircraft could be seen Sunday evening from roads around the airport.

Although the United States and Cuba are bitter Cold War foes, Cuba has a tradition of hospitality and is a signatory to international aviation accords.

On the day of the 9/11 attacks in New York and Washington, Havana offered to let the United States use its landing fields because US airports were in a state of chaos. Washington did not take Cuba up on the offer.

There are frequent charter flights back and forth between the two countries and a terminal in Havana is dedicated to receiving planes from the United States.