After deadly coordinated attacks on packed commuter rail trains in India, New York City officials upped security measures on the subways, sending hundreds of additional police officers to patrol and conduct random bag searches.
The New York Police Department said the measures were precautionary and there had been no specific threat to New York.
"We take a terror attack in any place in the world, especially one on a public transport system, as a serious warning," Mayor Michael Bloomberg said Tuesday.
The Metropolitan Transportation Authority, which runs the system, also announced increased security on its rail lines, tunnels and bridges and in Grand Central Terminal and Pennsylvania Station.
In Washington DC, the Metro service was not increasing police presence because of the Bombay bombings, spokeswoman Cathy Asato said. However, officers were donning high-visibility vests, and announcements urging travelers to be alert for suspicious activity were being played more frequently, she said.
Department of Homeland Security Secretary Michael Chertoff said there were no plans to raise the nation's threat level.
"At this time, there is no specific or credible intelligence suggesting an imminent threat to the homeland or our transit systems," he said in a statement.