A US rights group on Tuesday filed a lawsuit against the CIA on behalf of a German man whose secret detention dominated talks between German and US leaders.
US Secretary of State Condoleezza Rice admitted during talks with German Chancellor Angela Merkel in Berlin on Tuesday that the United States had made a mistake in the case of Khaled el-Masri, Merkel said.
Masri, a Lebanese-born German, alleges he was wrongfully abducted as a terrorism suspect in Europe and sent to Afghanistan for interrogation.
The landmark lawsuit filed by the American Civil Liberties Union (ACLU) is the first to challenge the Central Intelligence Agency over its handling of "war on terror" secret detainees.
It charges that the CIA violated US and universal human rights laws when it authorised agents to abduct Masri and hold him for five months in Afghanistan in what turned out to be a case of mistaken identity.
The ACLU said that Masri, 42, had flown to the United States on Saturday for the case but was stopped at Atlanta airport and put on a plane back to Germany.
The lawsuit was filed in the US District Court in Washington as the US secretary of state held talks in Berlin with the German chancellor.
Merkel's government has come under intense pressure to explain whether German authorities had helped the CIA cover up Masri's case.
The chancellor said Rice had admitted during their meeting that the United States had made a mistake in Masri's case.
"We talked about this one case which, of course, was accepted as a mistake by the US administration," Merkel told reporters. "I'm glad that Rice told me that mistakes would be corrected."
There has been widespread condemnation in Europe of reports of secret CIA prisons, known as "black sites", used to interrogate and allegedly torture terror suspects after the September 11, 2001 attacks on the United States.
The agency also allegedly used airports across Europe to transport the suspects.
US officials have consistently refused to confirm the existence of the covert prisons or flights while defending the US right to adopt tough anti-terrorism tactics.
Masri, an unemployed car salesman, told a press conference via satellite link he was detained on December 31, 2003 as he was heading on a bus to Macedonia for a holiday following a dispute with his wife.
He alleged that when the bus reached the Serbia-Macedonia border, guards confiscated his passport and detained him on suspicion he was linked to the al Qaeda terror network. Masri said he was drugged before being put on a plane to Afghanistan where he was held at a secret CIA prison and interrogated for several months.