"We should be able, in the 21st century, to sign global agreements," Merkel told the weekly Welt am Sonntag newspaper.

"If digital communication raises new questions worldwide, then we should take up the challenge. Germany is working for that," she said when asked whether an agreement modelled on the Kyoto Protocol that sets binding obligations on industrialised countries to reduce emissions of greenhouse gases was possible.

"This must be our goal, however ambitious it may be."

Merkel, who faces re-election in September 22 elections, has been under pressure for weeks to come clean with voters on what she knew about the US online surveillance.

She remains the frontrunner for the vote, and a new poll suggests the snooping affair is not yet a major election issue -- but the opposition hopes this will change while the media are turning increasingly hostile.

The issue is sensitive for Merkel, who said last week she only learnt about the scope of the US National Security Agency (NSA) snooping through media reports.

Many Germans are angry that their emails, phone calls, web searches and other data have been captured and stored under the NSA programme.

In an interview with public ZDF television, Interior Minister Hans-Peter Friedrich called on the United States on Friday to provide detailed information on the NSA's PRISM programme.

He said experts from several European countries and the United States would meet in Brussels on Monday to discuss the issue.

Snowden, whose passport has been revoked by Washington, has been marooned in Moscow airport's transit zone for the past three weeks, as he seeks asylum in a bid to evade US espionage charges for his leaks.

Snowden remains in transit as Washington steps up pressure

Whistle blower Snowden granted temporary access to Russia

Snowden's month in Moscow

(Voice of Russia, AFP)