The United States has ordered governments around the world to obey a new US requirement placing armed sky guards on some flights.
Homeland Security Secretary Mr Tom Ridge said the US would enforce the armed guards requirement and also assured Americans concerned about holiday air travel that aviation in the United States since September 11th, 2001, "has risen to new heights of security".
The new directive Mr Ridge outlined requires selected international flights that cross into US airspace to carry an armed law enforcement officer aboard.
The Homeland Security Department required such officers on flights where intelligence information led to a specific concern about that plane, a department spokesman said.
"We will then notify the carrier that, based on information we received, we require a law enforcement officer to be on the plane," he said.
"In the past, no country has ever tried to impose on other countries any measures of aviation security," said Mr Rafi Ron, president of New Age Security Solutions, a Washington-based consultancy, and the former security director for the Israeli Airport Authority.
Mr Ron predicted that despite concerns about armed air marshals expressed by British pilots and others, the measure would be enforced without much resistance because of the huge importance of the US market to foreign carriers.
AP