"We are asking international air carriers to take the protective action as part of our ongoing effort to make air travel safe for Americans and visitors alike," Homeland Security Secretary Tom Ridge said in a statement.
Homeland Security Department spokesman Dennis Murphy said US officials would notify foreign carriers when air marshals are needed.
"It is on a flight-by-flight basis. We will notify airlines when we have information on a specific flight," he told AFP.
Murphy said the carrier's country would have to provide the law enforcement personnel who are to be armed, trained and qualified to protect the passengers, crew and the plane.
The rule "requires the same level of cooperation from all airlines," he said. "We are getting voluntary cooperation from several airlines. This makes cooperation mandatory, not voluntary."
A total of six Air France flights - three to Los Angeles from Paris and three returning to Paris - were cancelled on Christmas Eve and Christmas Day at the request of US officials, amid fears that the planes could be used as weapons against US targets.
The new requirement was issued under an emergency amendment to existing regulations and applies to all passenger and cargo planes, Homeland Security said.
British pilots unhappy
The US announcement came a day after Britain said it was deploying an unspecified number of armed sky marshals on British passenger planes "in response to the present heightened state of alert in the USA."
But the plans to put gun-toting sky marshals on board British airliners flew into turbulence when British Airways and the main pilots' union said it would do more harm than good and put passengers at risk.
Air France flights to USA were last
week grounded due to terror alert
"Air marshals will be deployed where appropriate," said a joint statement from Transport Secretary Alistair Darling and Home Secretary David Blunkett.
But a spokeswoman for British Airways, one of the world's biggest air carriers, said: "We have always said we have concerns about having armed people on aircraft."
"We feel it is best to have strong security on the ground and that is where the focus of attention should be," she said.
"We have always been of the opinion that if it is not safe to fly then we will not fly."
Another airline spokesman added: "We have reservations about this. If you bring arms on to a plane then you raise the level of danger."
"Introducing a weapon into a cabin could lead to that weapon being used against passengers," he added.
"If the level of risk is so high that a sky marshal has to be deployed, then it would be easier to just not operate that particular flight."
"We have reservations about this. If you bring arms on to a plane then you raise the level of danger"
The British Air Line Pilots Association (BALPA) said it was never consulted on the measures - the latest in a series introduced in the wake of the September 11 attacks.
"We cannot agree with the government's decision to put armed guards on aircraft as we believe this will do more harm than good," said BALPA's General Secretary Jim McAuslan.
"We do not want guns on planes."