RIO DE JANEIRO (Reuters) – The journalist who first published secrets leaked by fugitive former U.S. intelligence agency contractor Edward Snowden vowed on Monday to publish more documents and said Britain will be “sorry” for detaining his partner for nine hours.

British authorities used anti-terrorism laws on Sunday to detain David Miranda, partner of U.S. journalist Glenn Greenwald, as he passed through London’s Heathrow airport.

Miranda, 28, a Brazilian citizen, said he was questioned for nine hours before being released without charge, minus his laptop, cellphone and memory sticks, which were seized.

Greenwald, a columnist for Britain’s the Guardian newspaper who is based in Rio de Janeiro, said the detention was an attempt to intimidate him for publishing documents leaked by Snowden disclosing U.S. surveillance of global internet communications.

Snowden, who has been granted asylum by Russia, gave Greenwald from 15,000 to 20,000 documents with details of the U.S. National Security Agency’s surveillance programs.

“I will be far more aggressive in my reporting from now. I am going to publish many more documents. I am going to publish things on England too. I have many documents on England’s spy system. I think they will be sorry for what they did,” Greenwald, speaking in Portuguese, told reporters at Rio’s airport where he met Miranda upon his return to Brazil.

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