LONDON — A British resident released from Guantanamo Bay after nearly five years in captivity said yesterday that his detention at the American prison camp was “profoundly difficult” to endure, his first comments since his release.

Bisher al-Rawi, an Iraqi national, had been held at the U.S. base in Cuba since it opened in 2002, but he was reunited with his family in South London this weekend.

British officials have long refused to represent resident foreigners held at Guantanamo, but they took up Mr. Rawi’s case after it was disclosed that he had provided assistance to MI5 — Britain’s domestic spy agency.

U.S attorney George Brent Mickum IV said Mr. Rawi had agreed, during one of at least six interviews with British agents at Guantanamo, to work for the British service in exchange for his release.

Foreign Secretary Margaret Beckett said Thursday that Mr. Rawi’s release had been agreed, but officials and lawyers have not disclosed precisely when the detainee was freed and flown to Britain.

“After over four years in Guantanamo Bay, my nightmare is finally at an end,” Mr. Rawi said in a statement. “I also feel great sorrow for the other nine British residents who remain prisoners in Guantanamo Bay.”

Britain’s Foreign Office said only five foreign nationals resident in Britain are held at the prison camp, in Cuba. Mr. Rawi said some detained British residents had gone on hunger strike to protest their extended solitary confinement.

“The extreme isolation they are going through is one of the most profoundly difficult things to endure. I know that all too well,” Mr. Rawi said.

Mr. Rawi and another British resident, Jamil el-Banna, were alleged to have been associated with Al Qaeda through their connection with the London-based radical Muslim cleric Abu Qatada. Mr. Rawi had lived in Britain since 1985, and Mr. Banna was granted refugee status in Britain in 2000.

“The hopelessness you feel in Guantanamo can hardly be described. You are asked the same questions hundreds of times,” Mr. Rawi said. “Allegations are made against you that are laughably untrue, but you have no chance to prove them wrong. There is no trial, no fair legal process.”

The two were arrested in 2002 in Gambia while trying to return to Britain with electronic equipment that authorities described as suspicious. The men’s lawyers claim it was a battery charger. Their lawyers have said the two were arrested after British intelligence agents passed on information about their travel plans to America.

“Leaving my best friend Jamil el-Banna behind in Guantanamo Bay makes my freedom bittersweet,” Mr. Rawi said in his statement. “He too should be released and reunited with his family.”

Lawyers claim that after their arrests in 2002, the men ended up in American custody. From Gambia, the CIA took them on a rendition flight to Cairo, Egypt, where the plane refueled, then to a CIA facility in Afghanistan, where they were held and interrogated as suspected terrorists, Mr. Mickum has said.

Mr. Rawi claimed in his statement that he and Mr. Banna were held in a CIA underground prison close to Kabul, before being transferred to Guantanamo Bay.