Picture of David Miranda (first from left) at Rio de Janeiro's Tom Jobim international airport
The United States said it had not asked Britain to detain the partner of one of the first reporters to publicise leaks about vast US spying programs.
David Miranda, the partner of the Guardian correspondent Glenn Greenwald, was held for nine hours on Sunday in Heathrow airport under a controversial British counter-terrorism law.
Greenwald was among the first reporters to publicize information leaked by former IT contractor Edward Snowden about controversial phone and Internet surveillance conducted by the US National Security Agency.
"There was a heads up that was provided by the British government, so this is something we had an indication was likely to occur," White House deputy spokesman Josh Earnest told reporters.
"But it's not something that we requested, and it's something that was done specifically by the British law enforcement officials."
He went on to refer to it as a "law enforcement action that was taken by the British government," adding that "the United States was not involved in that decision or in that action."
Greenwald has accused British authorities of trying to intimidate him over his reporting on Western intelligence programs and has vowed to reveal new information about London's spying apparatus.
"This was obviously designed to send a message of intimidation to those of us working journalistically on reporting on the NSA and its British counterpart, the GCHQ (Government Communications Headquarters)," Greenwald wrote in the Guardian.
Miranda was held and questioned by British authorities as he passed through Heathrow on his way back to Rio de Janeiro from a trip to Berlin.
"There were six different agents, coming and going, talking to me. They asked me questions about my whole life, about everything, and they took my computer, my games, my memory cards, everything," Miranda told reporters in Brazil on Monday.
Miranda, 28, often assists Greenwald with his work, the Guardian said.
He is not an employee of the newspaper but it had paid for his flights. He had stayed in Berlin with Laura Poitras, a US filmmaker who has been working with the Guardian.
Police detained Miranda on the basis of a controversial British counter-terrorism law that allows authorities to hold a suspect for up to nine hours without showing probable cause.
The suspect must cooperate and answer questions or face criminal charges, and a lawyer may or may not be present.
The United States has charged Snowden with espionage, saying he compromised vital programs that had foiled dozens of terrorist attacks.
Snowden was granted asylum in Russia after fleeing to Moscow, despite US demands that he be returned to face trial.