A Somali man has appeared in court in New York, charged with assisting al-Qaeda and militants from Somalia's al-Shabab group.
Ahmed Abdulkadir Warsame was seized in the Gulf of Aden in April and was then interrogated for two months on a US warship before his trial in America.
It is a sign of how President Barack Obama's administration plans to deal with terrorist suspects captured abroad, a BBC correspondent says.
Mr Warsame pleaded not guilty.
'Double' interrogation
Mr Warsame was detained on 19 April, prosecutors say.
He is accused of providing support to the Yemeni-based militant group al-Qaeda in the Arabian Peninsula (AQAP) and also to al-Shabab militants.
Under interrogation by intelligence officials aboard the US warship, the suspect gave up what was described as important evidence about the relationship between the two militant groups, according to the Associated Press.
The news agency adds that after the interrogation was complete, the FBI began questioning Mr Warsame from scratch - in a way that could be used in court.
The fact that Mr Warsame was held during his interrogation on the warship is a sign of how the US plans to deal with terrorist suspects seized abroad, the BBC's Tom Burridge in Washington reports.
Having promised - and so far failed - to close Guantanamo Bay in Cuba, President Obama is unlikely to want to increase the prison population there, our correspondent says.
He adds that Mr Obama also said he would close the CIA's network of secret prisons abroad.
Mr Warsame's case also shows how the US government is intent on trying terrorist suspects arrested abroad in civilian courts in America.
