The White House has confirmed that it was given a “heads up” by British officials before they held the partner of Glenn Greenwald but denied they had asked Britain to detain David Miranda.
Miranda, 28, was detained on his way through London's Heathrow Airport on Sunday as he made his way to Rio de Janeiro, where he lives with the Guardian journalist who first reported on controversial American spy programmes.
Miranda was questioned under schedule 7 of the Terrorism Act 2000 which allows officers to stop, search, question and detain individuals at border areas.
Upon arrival at Rio de Janeiro airport, he revealed that agents confiscated his electronic possessions and questioned him about his “entire life”:
I remained in a room. There were six different agents coming and going. They asked questions about my entire life, about everything.
They took my computer, video game, mobile phone, my memory card. Everything.
It was reported that Mr Miranda was transporting documents from US whistleblower Edward Snowden about US surveillance programmes back to the journalist.
Mr Greenwald said the detention of his partner was a “profound attack on press freedoms” which intended to intimidate those who had been reporting on the US National Security Agency and GCHQ.
Greenwald was heavily involved in The Guardian's revelations that US security services had monitored phone calls and internet data through large companies.
It was also reported that Britain's electronic eavesdropping agency GCHQ had been covertly gathering information from the secret US spy programme
Former CIA technical worker Edward Snowden was revealed as the source behind the intelligence leaks.
Snowden, 29 was granted temporary asylum in Russia earlier this month.
The journalist warned that his reporting would become "far more aggressive", even hinting that he would publish information on England’s spy system.
The Guardian said it was "dismayed" at the detention before urging British authorities to clarify the situation.
Figures including the independent reviewer of terrorism legislation called on the police to justify the decision to detain Mr Miranda.