The US Department of Homeland Security is going to lower its terrorism alert level to "elevated" from "high" for buses, subways and trains on Friday - a month after raising it in response to bombings in London, two US government officials said.
The officials said the decrease in the threat level was expected to be announced later on Friday and would take place in the evening, after rush hour.
The department had raised the alert level on July 7, after bombings on the London transport system killed more than 50 people.
Homeland Security spokeswoman Katy Montgomery would not confirm the change in threat level to "yellow" or "elevated" for mass transit from "orange" which represents a high level of risk.
"At this time, the mass transit system remains at orange, but it is reviewed several times every day," she said.
Last month, Homeland Security Secretary Michael Chertoff said the increase in the threat level was being made in the short term because of fears of a possible copycat attack.
At the time, Chertoff had said there was no specific, credible information of an imminent attack on the United States but has said that al Qaeda and its affiliates remained determined to target Europe and the United States.
The increase state of alert on mass transit meant more police were on watch and patrolling stations and platforms.