British authorities used anti-terrorism powers on Sunday (August 18) to detain the partner of a journalist with close links to Edward Snowden, the former U.S. spy agency contractor who has been granted asylum by Russia, as he passed through London's Heathrow airport.

The 28-year-old David Miranda, a Brazilian citizen and partner of U.S. journalist Glenn Greenwald who writes for The Guardian newspaper, was questioned for nine hours before being released without charge, a report on the Guardian website said.

A British Metropolitan Police Service spokesman said a 28-year-old male had been detained at Heathrow airport under provisions of the 2000 Terrorism Act.

That law gives British border officials the right to question someone "to determine if that individual is a person concerned in the commission, preparation or execution of acts of terrorism."

Rio de Janeiro-based Greenwald has interviewed Snowden and used 15,000 to 20,000 documents that Snowden passed to him to reveal details of the U.S. National Security Agency's surveillance methods.

Miranda was returning to Brazil from Berlin and was in transit at Heathrow, Greenwald said in a column posted on the Guardian website. He said British authorities seized his partner's laptop, mobile phone and USB sticks.

"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," Greenwald wrote, referring to Britain's Government Communications Headquarters.

A statement from the Guardian said it was "dismayed" at Miranda's detention and that it would be pressing British authorities for an urgent clarification.

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