Farooque Ahmed, 34, of Ashburn, was taken into custody early in the morning after a federal grand jury returned a three-count indictment on Tuesday against the naturalised US citizen who was born in Pakistan.
A Virginia man who allegedly believed he was helping al-Qaeda plan bombings at Washington area Metrorail stations was arrested on Wednesday, the justice department said.
Farooque Ahmed, 34, of Ashburn, was taken into custody early in the morning after a federal grand jury returned a three-count indictment on Tuesday against the naturalised US citizen who was born in Pakistan.
Federal officials said that the public was never in any danger during the investigation and that federal authorities had closely monitored Ahmed's activities until his arrest.
Earlier this month, the United States and Britain warned of an increased risk of terrorist attacks in Europe, with Washington saying al-Qaeda might target transport infrastructure.
A US official, on condition of anonymity, said there was "no connection between recent reports of the terrorism threats in Europe and this arrest."
Ahmed was charged with trying to provide material support to a designated terrorist organisation, collecting information to assist in planning a terrorist attack on a transit facility, and attempting to provide material support to help carry out multiple bombings to cause mass casualties at DC-area Metrorail stations.
A law enforcement official said that Ahmed was passing the information to someone who was working with law enforcement.
If convicted, he faces a maximum penalty of 50 years in prison, the justice department said.
"Farooque Ahmed is accused of plotting with individuals he believed were terrorists to bomb our transit system, but a coordinated law enforcement and intelligence effort was able to thwart his plans," said David Kris, assistant attorney general for national security.
"It's chilling that a man from Ashburn is accused of casing rail stations with the goal of killing as many metro riders as possible through simultaneous bomb attacks," US attorney Neil MacBride said.
From April to October 25 Ahmed allegedly conducted surveillance, videotaped, photographed, and drew diagrams of the Arlington Cemetery, Courthouse, Crystal City and Pentagon City Metrorail stations, and offered suggestions about where to place explosives to kill people in simultaneous attacks planned for 2011, the indictment said.
He allegedly told an individual whom he believed to be affiliated with al-Qaeda that between 4pm and 5pm would be the best time for an attack to cause the most casualties, the indictment said.
Since the September 11, 2001, attacks, US authorities have worried about another attack on US soil.
Last week, a Jordanian national was sentenced to 24 years in prison for attempting to blow up a Dallas skyscraper.
Earlier this month, Pakistani-born American Faisal Shahzad was sentenced to life in prison for trying to set off a car bomb in New York's Times Square.
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