David Miranda, the partner of Guardian columnist Glenn Greenwald, was detained Sunday morning by U.K. authorities in London's Heathrow airport under the Terrorism Act, according to The Guardian.

The 28-year-old was released nine hours later without being charged, but some of his electronics were confiscated. Miranda was traveling from Berlin to Rio de Janeiro, his home.

"This is a profound attack on press freedoms and the news gathering process," said Greenwald. "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 broke the story about mass telephone and Internet surveillance being conducted by the National Security Agency (NSA) thanks to information provided by former contractor Edward Snowden. Greenwald said he had received more than 15,000 secret U.S. documents from Snowden.