Anonymous telephone threats against commercial airliners, possibly from the same source, caused a scare on Monday involving four international flights at airports in New York and New Jersey.
Authorities said the threats did not appear to be credible. They described searches done on three of the jets as a precaution.
In one instance Monday morning, US military jets escorted an Air France flight into New York City after someone claimed a chemical weapon was aboard the aircraft, the FBI said.
"Out of an abundance of caution, Air France flight number 22 was escorted to John F. Kennedy airport by U.S. Air Force fighter jets following a phone threat," the FBI said in a statement. "There were no incidents or hazards reported on board the flight by either the passengers or its crew. The plane has been cleared."
A Saudi Arabian Airlines flight arriving at Kennedy also was being checked out because of another threat, authorities said.
A third threat was made against an American Airlines jet flying from Birmingham, England, to Kennedy while it was still in the air, said airline spokesman Kent Powell. Authorities initially told the pilot to land and taxi to a remote area away from the terminal but later radioed that the threat was not credible and cleared the plane to go to the terminal, Powell said.
At Newark Liberty International Airport, passengers were removed from a United Airlines flight after it arrived from Madrid, said United spokeswoman Mary Clark. The plane was being inspected Monday afternoon at a spot away from the terminal.
Maryland State Police said they received an anonymous call at the McHenry barracks in the western part of the state threatening commercial aviation about 6:30 a.m. Monday and referred it to the FBI. They declined to comment further.
Associated Press writer David Koenig in Dallas contributed to this report.