LONDON (AP) — The first Guantanamo detainee released since President Barack Obama took office returned to Britain on Monday, saying his seven years of captivity and torture at an alleged CIA covert site in Morocco went beyond his "darkest nightmares."

Binyam Mohamed's allegations — including repeated beatings and having his genitals sliced by a scalpel — have sparked lawsuits that could ensnare the American and British governments in protracted court battles.

Looking frail from a hunger strike, Mohamed, who once was accused by U.S. authorities of being part of a conspiracy to detonate a bomb on American soil, stepped off a charter plane and was whisked away by police, border control agents and immigration officials.

The 30-year-old Ethiopian refugee, who moved to Britain as a teenager, was freed after four hours of questioning.

Attorney General Eric Holder, who traveled Monday to Guantanamo Bay as the Obama administration weighs what is needed to shut the facility, thanked Britain for its cooperation in the case.

"The friendship and assistance of the international community is vitally important as we work to close Guantanamo, and we greatly appreciate the efforts of the British government to work with us on the transfer of Binyam Mohamed," he said.

Lawyers for Mohamed are seeking secret U.S. intelligence and legal documents they say will prove the Bush administration sent Mohamed to Morocco, where it knew he would be tortured. They claim the documents also prove Britain was complicit in the abuse.

Unlike in the U.S., Britain's leaders don't have a past government to blame — Prime Minister Gordon Brown's Labour Party has been in power for more than a decade.

But the case is also a test for Obama. While he has promised Guantanamo's closure and an end to torture, he has not yet publicly explained how his government will change the process of extraordinary renditions, which involve sending terror suspects to foreign countries to be interrogated.

CIA Director Leon Panetta has told Congress renditions could continue, but that prisoners won't be handed over to countries where they are likely to be tortured — which has always been the stated U.S. policy.

The Bush administration's extraordinary rendition program was much criticized, in part because some prisoners were handed over to countries with documented histories of human rights abuses. Morocco was one such country, according to an Amnesty International report.

The United States refuses to account for the 18 months Mohamed says he was in Morocco.

In a statement released Monday by his attorneys, Mohamed said: "I have been through an experience that I never thought to encounter in my darkest nightmares."

"Before this ordeal torture was an abstract word to me…It is still difficult for me to believe that I was abducted, hauled from one country to the next and tortured in medieval ways all orchestrated by the United States government." He said he would not make any media appearances until he had recovered from his ordeal.

Britain's Foreign Secretary David Miliband said he was pleased with Mohamed's return. The British government has been fighting for his release since 2007.

Mohamed has few remaining ties to Britain, and authorities say there's no guarantee he'll be allowed to stay since his residency expired in 2004. He will have to report regularly to police and volunteered to other restrictions that will limit his foreign travel.

Mohamed's parents are back in Ethiopia and his siblings live in the United States. His sister, Zuhra Mohamed, traveled to Britain for her brother's release and said: "I am so glad and so happy, more than words can express."

It is unlikely any of Mohamed's accused interrogators will be prosecuted because the worst abuse allegedly occurred in Pakistan and Morocco. But any British or American officials found to have known about his rendition or any mistreatment could face civil or criminal charges.

Mohamed has said he was interrogated by at least one British security agent from MI5 in Pakistan and that British intelligence officials fed material about his time in Britain to his interrogators in Morocco.

"Many have been complicit in my own horrors over the past seven years," his statement said Monday. "The very worst moment came when I realized in Morocco that the people who were torturing me were receiving questions and materials from British intelligence."

According to Mohamed's account, which The Associated Press obtained from his lawyers in 2006, he converted to Islam in 2001 and went to Afghanistan and Pakistan, where he said he wanted to experience a traditional Islamic society and get away from a bad circle of friends in London as he tried to kick a drug habit.

He was arrested in Pakistan in 2002 for trying to return to Britain on a false passport and held in Karachi for three months, during which time he said he was beaten, hung by his wrists from a leather strap and questioned by at least one MI5 agent.

Mohamed claims the Americans then sent him to Morocco, where he endured 18 months of torture, including the genital mutilation. He was then sent to another alleged CIA detention site in Afghanistan before arriving in Guantanamo in 2004.

He was charged in May 2008 with conspiring to fill U.S. apartments with natural gas and blow them up — charges he said he only confessed to after more than two years of torture.

The charges were dropped without explanation in October 2008 — but only after the prosecutor in his planned military trial quit and accused the U.S. government of withholding evidence. Lawyers in Britain filed a lawsuit for the disclosure of 42 secret U.S. intelligence documents they said would prove any evidence was obtained under torture.

Two British judges have reopened the case and Britain's attorney general is investigating whether there was criminal wrongdoing on the part of Britain or the MI5 agent who interrogated Mohamed in Pakistan.

Several other lawsuits are under way in the United States against a Boeing subsidiary that allegedly supplied planes for rendition flights to Morocco and for the disclosure of Bush-era memos on renditions and interrogation tactics.

Some criticized Mohamed's release, saying Monday that no detainees should have been freed before their status was reviewed under an executive order Obama issued last month.

"President Obama ordered a 180-day review to determine the status of the detainees, so it's unclear to me why Mr. Mohamed has been released without such a review," said retired Navy Cmdr. Kirk Lippold who was in charge of the USS Cole when it was attacked by suicide bombers in 2000.

"Everyone is interested in the rights of detainees but where are the rights for the families of my 17 sailors who were killed?"

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Associated Press Writer Pam Hess contributed to this report from Washington.