The Bush administration called for heightened security on U.S. mass transit systems by raising the terrorism threat level to "orange" in response to todays bombings of subway trains and buses in London.
The heightened alert, the Associated Press reported, will apply to "regional and intercity passenger rail, subways and metropolitan bus systems," Homeland Defense Secretary Michael Chertoff said.
Governors and other officials around the country asked public transportation riders to exercise increased vigilance.
Chertoff said he did not know of any credible evidence of a planned attack in the U.S. and that travelers should not change their travel plans.
At last report, bomb blasts during todays morning rush hour killed at least 33 people riding buses and subway trains in London.