STOCKHOLM – Sweden has been a key partner for the United States in spying on Russia and its leadership, Swedish television said on Thursday, citing leaked documents from the U.S. National Security Agency (NSA).

Earlier this year, former U.S. National Security Agency contractor Edward Snowden passed to media details of a global spying programme by the NSA, stirring international criticism. The U.S. has said much of the information was a result of cooperation with other intelligence services.

Swedish television cited a document dated Apr. 18 this year saying Sweden's National Defence Radio Establishment (FRA), which conducts electronic communications surveillance, had helped in providing the United States with information on Russia.

"The FRA provided NSA ... a unique collection on high-priority Russian targets, such as leadership, internal politics," it quoted the document saying.

The FRA declined to comment on the matter.

"We do in general have international cooperation with a number of countries, which is supported in Swedish legislation, but we do not comment on which ones we cooperate with," Anni Bolenius, head of communications at the FRA said.

In a separate document, high level NSA employees were told to "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."

Previously, Sweden's FRA has said only that it cooperates with foreign intelligence services, but that all activities are strictly controlled by Swedish law.

Swedish television said it had obtained the documents from Glenn Greenwald, the journalist who brought the Snowden leaks to world attention.

Snowden is in Russia, where he was granted asylum in August for at least a year.