Leaked documents from whistleblower Edward Snowden revealed on Wednesday that Sweden helps the US spy agency keep tabs on Russian politicians.
Information on Russian politicians was collected by Sweden's main signals intelligence agency, the National Radio Defence Establishment (Försvarets radioanstalt, FRA), and was then handed over to the NSA, Sveriges Television (SVT) revealed.
The information was no shock for Sweden's defence minister.
"The fact that we have this cooperation is completely natural," Karin Enström told the TT news agency.
She added that such espionage was necessary.
"We need to be able to carry out intelligence operations to be able to protect Sweden against further threats. We have an operation that is carried out within the framework of the FRA, with clear legislation, strict control, and parliamentary oversight," she added.
"But how it is carried out and with whom Sweden cooperates are not public information."
She added that the government "obviously" takes part in the operations: "That's the whole point. It's also obvious that we know who we are cooperating with. However, we have chosen not to comment on which countries FRA has cooperated with."
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Allan Widman, a Liberal Party (Folkpartiet) MP and the party's defence policy spokesman, said that it amount to "professional misconduct" if Sweden's didn't know what was happening in Russia, but that cooperation with the US was more problematic.
"Swedish law does not allow any foreign authority to order notifications from the FRA," he told the Svenska Dagbladet newspaper (SvD).
"However there is a possibility of collaboration between countries. No country has the possibility to manage alone, therefore it's not surprising that the US and Sweden should work together."
Lund University professor and intelligence expert Wilhelm Agrell said the documents detailed in the SVT report confirm what has previously been gleaned through second-hand information: that FRA and the NSA have a close working relationship when it comes to monitoring leaders in Russia.
"Based on these documents that are cited, it appears the foreign connection was much more central and perhaps the driving factor behind the FRA law," he told the TT news agency in reference to the 2008 law that gave the agency the authority to monitor cable-bound communications traffic that crossed Sweden's borders.
Left Party MP and foreign policy spokesman Hans Linde plans to call Foreign Minister Carl Bildt to parliament for an explanation.
"If it's the case that American interests have been in control, that the US has asked Sweden to collect this information, then that goes outside the mandate given by Swedish legislation governing FRA," he told TT.