Singer-songwriter and peace activist Yusuf Islam, formerly known as Cat Stevens, is to begin legal action against US authorities to find out why he was deported from the United States as a terrorist risk, he said. We have now initiated a legal process to try to find out exactly what is going on, and to take all necessary steps to undo the very serious, and wholly unfounded, injustice which I have suffered," the ex-singer said in a statement. Islam, 57, who gave up his hugely successful pop career in the late 1970s when he became a Muslim, arrived back in London on Thursday after being swiftly removed from the United States. He had been travelling to Washington on Tuesday when his flight was diverted to Bangor, Maine where he was detained on "national security grounds", according to US security officials. Asa Hutchinson, the US Department of Homeland Security's under secretary for border and transportation security, refused to say what allegations had been made against Islam, but stressed the action was taken due to "a connection to some type of terrorist activity". Islam was denied entry to Israel in 2000 over suspicions that he had given money to the radical Palestinian group Hamas, but has consistently condemned terrorism and denied supporting it. In his statement, Islam described his deportation as a "dark episode". "Never would I believe that such a thing could happen in the land of the free - unfortunately, it did," he said. **PHOTO CAPTION*** Singer-songwriter and peace activist Yusuf Islam speaks to journalists at London's Heathrow airport. (AFP/Alessandro Abbonizio)