The Homeland Security Department said the directive, which is effective immediately, will further enhance security on commercial and cargo aircraft flying to, from and over the United States.
"We are asking international air carriers to take this 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.
"I have said that we will take specific steps to increase security whenever necessary, and with this action we are doing just that," he added.
A Homeland Security official tells CBS News that if a foreign carrier or country refuses to place an armed guard on flights as requested by the United States, those flights will be barred from landing at American airports.
The official says the new policy is a direct response to the kinds of threats that led to the abrupt cancellation of several Air France flights on Christmas Eve, reports CBS News Correspondent Peter Maer.
Homeland Security spokesman Dennis Murphy said the move will apply to specific flights "based on specific information" whenever it surfaces.
The decision will be based on intelligence analysis of each flight's passenger and crew list.
"We will then notify the carrier that based on information we received, we require a law enforcement officer to be on the plane," Murphy said. The directive contemplates that armed officers from the country of the airline's ownership would be aboard.
Murphy says the U.S. will require "trained, armed law enforcement officers who will be in the position to defend the aircraft as necessary."
A senior intelligence official said earlier this month that analysts were particularly concerned about the threat of Sept. 11-style attacks, in which terrorists would use hijacked airliners as weapons.
The directive comes in the form of three emergency amendments to air security regulations involving cargo planes, passenger planes and airliners passing over U.S. airspace.
There are thousands of international commercial and cargo flights daily involving U.S. airspace and hundreds of international carriers.
Britain said Sunday it tightened security for trans-Atlantic flights and suggested it might put armed sky marshals on some planes. The United States already places armed security officers on certain flights.
"The last few days have seen the United States increase their general threat and security levels, and what we are proposing is a proportionate and appropriate level of response at a time when the threat to both our countries and around the world remains real and serious," Britain's top law enforcement official, David Blunkett, said.
The Bush administration raised the terrorism alert level to orange, or high, on Dec. 21 and Air France canceled six flights between Paris and Los Angeles on Wednesday and Thursday, following security discussions between U.S. and French officials.
"What we are saying here is we expect this level of cooperation from all nations," Murphy told The Associated Press. "This step is in case we might not get that same level of cooperation that we've received thus far from our closest allies. We anticipate the same level of cooperation from all air carriers that fly to and out of the U.S."
In a news release, the Homeland Security Department said it will continue to conduct checks on passengers and crew of flights entering and leaving U.S. airspace, and will analyze threat information related to those flights.
When intelligence information warrants, it said, the government will direct additional security requirements for specific flights, including protection by law enforcement officers where warranted, it said.
In a related development, CBS News' Larry Miller says a London newspaper reports Saudi Arabian authorities have arrested two men preparing to fly two light aircraft loaded with explosives into a packed a British Airways passenger jet.