Brazil says the detention under British terror laws of one of its citizens at London’s Heathrow airport caused “grave concern” and was “unjustified”.
David Miranda, the partner of Guardian journalist Glenn Greenwald who published documents leaked by Edward Snowden, was held at Heathrow for nine hours on his way to Rio de Janeiro.
He reportedly had his mobile phone, laptop, DVDs and other items seized.
Mr Miranda was later released by British authorities.
Mr Greenwald called his partner’s detention an “intimidation” and a “profound attack on press freedoms”.
Under the Terrorism Act 2000, UK police can hold someone at an airport for up to nine hours – but the power must be used appropriately and proportionately and is subject to independent scrutiny.
Amnesty International says the incident shows the law can be abused for what it described as “petty and vindictive reasons”.
“At 08:05 on Sunday 18 August 2013 a 28-year-old man was detained at Heathrow Airport under Schedule 7 of the Terrorism Act 2000. He was not arrested. He was subsequently released at 17:00,” said a statement issued by the Metropolitan Police.
Mr Greenwald said the British authorities’ actions in holding Mr Miranda amounted to “intimidation and bullying”.
“They never asked him about a single question at all about terrorism or anything relating to a terrorist organisation,” he told the BBC World Service’s Newsday programme.
“They spent the entire day asking about the reporting I was doing and other Guardian journalists were doing on the NSA stories.
“The principal point, since they kept him for the full nine hours, is to try and send a message of intimation and bullying.
“I don’t understand why they don’t realise that all it’s going to accomplish is the exact opposite effect – I’m going to report more aggressively and with a more emboldened mind,” Mr Greenwald told the BBC.
The Brazilian government issued an official statement soon after the release of Mr Miranda.
The foreign ministry document says there was no justification for detaining an “individual against whom there are no charges that can legitimate the use of that [anti-terror] legislation”.
It also says Brazil expects incidents “such as the one that happened to the Brazilian citizen today” not to be repeated.
Mr Miranda was flying back from the German capital, Berlin, to Rio de Janeiro, where he lives with Mr Greenwald, when he was detained in transit through Heathrow.
In Germany, he had met US film-maker Laura Poitras, who has also been working on the Snowden files with Mr Greenwald and The Guardian. according to the newspaper.
Following his detention at Heathrow, Brazilian government officials and Guardian lawyers were called to the airport, The Guardian says.
The NSA has broken privacy rules and overstepped its legal authority thousands of times in the past two years, according to documents leaked by Edward Snowden.
The incidents resulted in the unauthorised electronic surveillance of US citizens, it is alleged.
Mr Snowden, a former NSA contractor, has leaked top secret documents to the US and British media.
He has been given asylum in Russia.