In an open letter to Prime Minister David Cameron, which was published Sunday, the editors said locking up David Miranda was a blow to global press freedom and brought Britain's reputation as a "stout defender of democracy and free debate."
The letter, which was published in the British newspaper Observer, did not mention Miranda by name. Miranda is the partner of Guardian reporter Glenn Greenwald, who worked with Snowden in leaking classified information from the U.S. National Security Agency.
Miranda was detained at London's Heathrow Airport for several hours as he attempted to fly to Brazil. No charges were filed; however a criminal investigation into Miranda was launched.
"It is deeply disturbing that the police have now announced a criminal investigation," the editors said in their letter. "We hope this is not to be seen as a step against journalists doing journalism."
Norway's NRK said the editors viewed the Miranda investigation as an unwelcome incident of a government using anti-terrorism laws to muzzle the media.
The editor of NRK was not among the four signers of the letter. Those editors represented Norway's Aftenposten; Dagens Nyheter of Sweden; Helsingen Sanomat of Finland and Denmark's Politiken.