David Michael Miranda, the partner of journalist Glenn Greenwald, was detained by British police for nine hours at Heathrow airport Sunday as he was on his way to a flight back to Brazil. Greenwald is the Guardian reporter who has published NSA documents from Edward Snowden.

The Guardian reported that Miranda was told by police that he would be held under Section 7 of the Terrorism Act 2000, which allows officers to stop, search or detain anyone for up to nine hours. The controversial law states that after nine hours, the person has to be formally arrested or released and over 97 percent of those detained are held for less than an hour.

According to the New York Times, Miranda had been in Berlin to help Laura Poitras, a documentarian going through Snowden’s documents. The 28-year-old was returning to Brazil, where he lives with Greenwald. He is a Brazilian citizen and the Guardian paid for the trip.

“This is a profound attack on press freedoms and the news gathering process,” Greenwald said. “To detain my partner for a full nine hours while denying him a lawyer, and then seize large amounts of his possessions, is clearly intended to send a message of intimidation to those of us who have been reporting on the NSA and GCHQ. The actions of the UK pose a serious threat to journalists everywhere.”

Greenwald added, “But the last thing it will do is intimidate or deter us in any way from doing our job as journalists. Quite the contrary: it will only embolden us more to continue to report aggressively.”

The Guardian also said it was “dismayed” by the news and that “We are urgently seeking clarification from the British authorities.” Scotland Yard only issued a standard statement confirming that a 28-year-old was held under the law.

Greenwald said that Miranda was giving Poitras new documents in exchange for documents from Poitras and all the documents exchanged were from Snowden. Miranda was carrying electronic media, including CDs and DVDs, which were seized by British authorities and not returned, said Greenwald.

Brazil’s government said it has “grave concern” that one of its citizens was detained. Amnesty International also issued a statement, noting, “There is simply no basis for believing that David Michael Miranda presents any threat whatsoever to the UK government. The only possible intent behind this detention was to harass him and his partner, Guardian journalist Glenn Greenwald, for his role in analysing the data released by Edward Snowden.”