British prime minister David Cameron has called on The Guardian and other newspapers to show "social responsibility" in the reporting of the leaked NSA files to avoid high court injunctions or other government measures to prevent the publication of information that could damage national security.
In a statement to MPs on Monday about last week's European summit in Brussels, where he warned of the dangers of a "lah-di-dah, airy-fairy view" about the dangers of leaks, Cameron said his preference was to talk to newspapers rather than resort to the courts.
But he said it would be difficult to avoid acting if newspapers didn't heed government advice.
Cameron issued the warning after Conservative MP Julian Smith quoted a report in The Sun newspaper that said Britain's intelligence agencies believe details from the National Security Agency files leaked by the US whistle-blower Edward Snowden have hampered their work.
The Sun quoted a "top surveillance source" as saying that terrorists have "gone quiet" after the publication of details about operations of the NSA and Britain's Government Communications Headquarters.
Cameron told MPs: "We have a free press; it's very important the press feels it is not pre-censored from what it writes and all the rest of it. The approach we have taken is to try to talk to the press and explain how damaging some of these things can be and that is why The Guardian did actually destroy some of the information and disks that they have. But they've now gone on and printed further material which is damaging.
"I don't want to have to use injunctions or D notices [defence advisory notices] or the other tougher measures. It's much better to appeal to newspapers' sense of social responsibility. But if they don't demonstrate some social responsibility, it would be very difficult for government to stand back and not to act."
The Guardian agreed to allow officials from GCHQ to oversee the destruction of hard drives in July, after the government threatened to use an injunction to block publication of information from the NSA files.
Editor-in-chief Alan Rusbridger said the destruction of the hard drives allowed The Guardian to continue reporting on the NSA files from its New York office.
The D-notice system is a voluntary code between British government departments with responsibility for national security and the media. A notice can be issued to the media to prevent "inadvertent public disclosure of information that would compromise UK military and intelligence operations and methods".
Parliament's intelligence and security committee announced earlier this month that it is to scutinise the extent of mass surveillance in response to the concerns raised by the Snowden leaks.
Cameron issued his warning to newspapers after Labour party leader Ed Miliband raised concerns over reports that the US monitored the phone of German Chancellor Angela Merkel.