WASHINGTON - A PAKISTANI-AMERICAN was arrested on Wednesday for plotting to cause carnage on Washington's subway system by carrying out bomb attacks with people he believed were tied to Al-Qaeda, officials said.

Farooque Ahmed, 34, had been allegedly observing, videotaping and photographing Metro stations in the Virginia suburbs of Washington, including stations at the Pentagon and Arlington National Cemetery, since April to plan the attacks, which would have been carried out next year.

He is alleged to have told contacts whom he met over the course of six months, and believed to be linked to Al-Qaeda, that he wanted to 'kill as many military personnel as possible' and suggested where bombs should be planted on Metro trains 'to kill the most people'.

'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,' David Kris, assistant attorney general for national security told reporters.

Ahmed, a naturalised US citizen who was born in Pakistan, appeared in a Virginia court on Wednesday afternoon to hear the charges against him.

They include attempting to provide material support to a terrorist organisation, collecting information to assist in planning a terrorist attack, and attempting to provide help to carry out multiple bombings and cause mass casualties in the Washington area. If convicted, he could be jailed for up to 50 years.

US man held in subway plot