British Transport police have been told to challenge more suspect passengers as security on London's Underground network was further increased after yesterday' bomb attacks.
And commuters on New York subways will be subjected to random searches of backpacks and packages, the city's police said.
However, the introduction of airport-style checks
on travellers in London has been ruled out as impractical on a system that carries three million people a day.
Andy Trotter, the Deputy Chief Constable of British Transport Police, said there would be more "intrusive policing", with an increase in uniformed and plain-clothes officers on trains and at stations.
The number of "stop and searches" of passengers would also be stepped up.
Mr Trotter said: "The public want us to do that; they want more suspicious people challenged."
The use of sniffer dogs will be increased and the numbers of CCTV cameras across the network will also be expanded.
Police are also investigating the use of other technology, such as portable metal detecting arches and hand-held sensors that can detect explosives.
A leading civil liberties group in the US said random searches ran counter to the country's Constitutional Fourth Amendment, which prohibits "unreasonable searches" without "probable cause".
Security on New York's transit system had already been stepped up since the first bombings in London on July 7, in which 56 people died when three underground trains and a bus were targeted by suicide bombers.
Stressing there was no new threat against the city's transit system, New York Police Commissioner Raymond Kelly said the searches would take place mostly at subway stations and possibly as people board city buses.
"We will be instituting random searches of packages and backpacks as people enter the transit system," Kelly said, adding that "no racial profiling will be allowed".
However, Donna Lieberman, executive director of the New York Civil Liberties Union, said, "The Fourth Amendment prohibits police from conducting searches where there is no suspicion of criminal activity.
"One of the dangers of random searches is that they can invite the possibility of racial, ethnic or religious profiling," she said.
A Quinnipiac University poll on Wednesday revealed that 72 per cent of New Yorkers fear an attack like the July 7 bombings in London would occur in New York.
New York has been on high alert for another attack since the September 11, 2001, hijacked plane attacks which felled the World Trade Centre twin towers and killed nearly 3000 people.
- INDEPENDENT, REUTERS
