WASHINGTON: A Pakistani-American man was sentenced Monday to 23 years in prison for plotting attacks on subway stations around the US capital with people he believed were Al-Qaeda affiliates.

Farooque Ahmed, a naturalised US citizen who lived in the Virginia suburbs of Washington, admitted photographing stations in 2010 to plan simultaneous bomb attacks.

The 35-year-old pleaded guilty to charges of attempting to provide material support to a designated terrorist organisation and collecting information to assist in planning a terrorist attack, US officials said.

A federal judge also sentenced Ahmed to 50 years of supervised release after prison, as part of a plea agreement between Ahmed's lawyers and prosecutors.

Ahmed was caught in a sting operation by US authorities, who said that “at no time was the public in danger during this investigation and that the FBI was aware of Ahmed's activities from before the alleged attempt began and closely monitored his activities until his arrest.”

Ahmed was arrested in October 2010. Authorities said he had studied security operations at subway stations, took photographs, and provided diagrams to the fake Al-Qaeda affiliates.

Ahmed also “provided suggestions as to where explosives should be placed on trains in Metrorail stations in Arlington to kill the most people in simultaneous attacks planned for 2011,” the US Department of Justice said in a statement.