Britain's GCHQ signals intelligence agency provided guidance to counterparts in Spain, France and Germany on how to engage in mass surveillance of telephone and internet communications, The Guardian said Friday.

Large-scale monitoring is conducted both through direct tapping of fiber-optic cables and via covert cooperation with telecoms firms, the British newspaper said, citing GCHQ documents provided by former U.S. intelligence contractor Edward Snowden.

"GCHQ played a leading role in advising its European counterparts how to work around national laws intended to restrict the surveillance power of intelligence agencies," the Guardian said.

The files from Snowden include a 2008 GCHQ appraisal of the surveillance capabilities of its European partner agencies.

The review praises the respective foreign intelligence agencies of Germany and France.

Germany's BND is said to have "huge technological potential and good access to the heart of the internet," while France's DGSE is described as "a highly motivated, technically competent partner."

The 2008 document indicates that the Spanish intelligence service, the CNI, had used its ties with an unnamed British telecoms firm to carry out massive internet surveillance.

"GCHQ has not yet engaged with CNI formally on IP (internet protocol) exploitation, but the CNI have been making great strides through their relationship with a UK commercial partner," the document says.

Spain, Germany and France have all demanded explanations from Washington about the U.S. National Security Agency's monitoring of phone and internet communications inside their borders.

Berlin, in particular, is incensed over revelations that NSA monitored the person cellphone of German Chancellor Angela Merkel.