STOCKHOLM (AFP) - Sweden has provided the United States with "unique" intelligence on Russia's leadership, according to new documents leaked by US fugitive Edward Snowden and revealed on Thursday by Swedish public broadcaster SVT.

The documents indicate that the US National Security Agency (NSA) sees Sweden's signals intelligence agency, FRA, as a "leading partner" in the surveillance of telecoms and Internet traffic, particularly from Russia.

"The FRA provided NSA... unique collection on high-priority Russian targets, such as leadership, internal politics," according to a document dated April 18, 2013 and obtained by SVT from the American journalist Glenn Greenwald who has published details of numerous NSA files leaked by Snowden.

Another document underlined Sweden's notable access to Russia's communication network thanks to cables passing through Swedish territory.

"Thank Sweden for its continued work on the Russian target, and underscore the primary role that FRA plays as a leading partner to Work the Russian Target, including Russian leadership... (and) counterintelligence. FRA's cable access has resulted in unique SIGINT (signals intelligence) reporting on all of these areas."

Mr Fredrik Wallin, a spokesman for the FRA, refused to confirm that Sweden had spied on the Russian leadership and said the suggestion that Sweden had a leading role was "very flattering".

Swedish Defence Minister Karin Enstroem told SVT it was no surprise that the country cooperated with other intelligence services.

"Sweden builds its security together with others," she said.

"But which countries and which methods we use are not public information."

Earlier this year British journalist Duncan Campbell alleged that Sweden was the British intelligence agency's "biggest partner" outside the English-speaking world.