RIO DE JANEIRO — An American journalist who has written stories based on documents leaked by former National Security Agency contractor Edward Snowden said Monday he’ll publish with more fervor after British authorities detained his partner.
London police detained David Miranda, who is in a civil union with reporter Glenn Greenwald, under antiterror legislation at Heathrow Airport in London Sunday.
Miranda arrived Monday in Rio de Janeiro, where he lives with Greenwald.
A defiant Greenwald promised he was going ‘‘to write much more aggressively than before’’ about government snooping.
‘‘I’m going to publish many more things about England, as well,’’ he said in Portuguese at Rio’s international airport when Miranda arrived. ‘‘I have many documents about England’s espionage system, and now my focus will be there, too. I think they’ll regret what they’ve done.’’
In Washington, White House spokesman Josh Earnest said that the US government was tipped off by UK counterparts that Miranda would be detained but that the United States had not requested the action. The Brazilian government objected to Miranda’s detention, saying it wasn’t based on any real threat.
Miranda said he wasn’t threatened while detained but confirmed that personal objects were taken from him.
“There were six different agents,’’ he said. ‘‘They asked questions about my whole life, about everything. They took my computer, video game, cellphone, memory thumb drives, everything.’’
In London, a British lawmaker called for police to explain why Miranda had been detained and why it took nearly nine hours to question him.
Miranda was held for nearly the maximum time that British authorities are allowed to detain individuals under the Terrorism Act’s Schedule 7, which authorizes security agencies to stop and question people at borders.
Keith Vaz, chairman of Parliament’s Home Affairs Select Committee, told the BBC that ‘‘you have a complaint from Mr. Greenwald and the Brazilian government — they indeed have said they are concerned at the use of terrorism legislation for something that does not appear to relate to terrorism. So it needs to be clarified, and clarified quickly.’’
Vaz said it was ‘‘extraordinary’’ that police knew Miranda was Greenwald’s partner and that the authorities were targeting partners of people involved in Snowden’s disclosures.
The case drew the ire of rights groups.
‘‘It’s incredible that Miranda was considered to be a terrorist suspect,’’ said David Mepham, the UK director at Human Rights Watch. ‘‘On the contrary, his detention looks intended to intimidate Greenwald and other journalists who report on surveillance abuses.’’
Britain’s laws are not unique. US customs officials can search the electronic devices of anyone entering the United States without a search warrant. According to a 2011 internal Homeland Security Department report, officers at the border can search the devices and in some cases hold on to them for weeks or months.
Greenwald has written about NSA surveillance programs based on files disclosed by Snowden, who now has temporary asylum in Russia.
Miranda, a 28-year-old university student, was traveling home to Brazil after visiting Germany, where he met with Laura Poitras, a US filmmaker who has worked with Greenwald on the NSA stories.