"It's very serious matter if Sweden is indeed involved in American surveillance programmes," Green Party IT policy spokeswoman Maria Ferm told The Local.
The comments come following claims that emerged on Thursday during a European Parliament hearing on the wiretapping scandal and come from investigative journalist Duncan Campbell, according to a report in the Metro daily.
Campbell said that Sweden's Swedish National Defence Radio Establishment (Försvarets radioanstalt, FRA) provided the United States National Security Agency (NSA) access to the Baltic underwater cables.
The Swedish MEPs who sit on the Committee on Civil Liberties (Libe), Social Democrat Anna Hedh and Cecilia Wikström of the Liberal Party, weren't present at the hearing when the Campbell mentioned Sweden's close partnership with both the NSA and British GCHQ.
Wikström was at an "important meeting", a spokesperson told the TT news agency, while Hedh's flight had been cancelled.
"I'm very concerned about the information that came up in the hearing," said Ferm.
"It's deeply troubling if Sweden is participating in surveillance operations that are as extensive as those of the United States and that attempt to circumvent national laws."
Sweden's Democracy Minister, Birgitta Ohlsson of the Liberal Party (Folkpartiet), was also alarmed by the revelations.
"I absolutely think this is not good. I've also been engaged in issues related to personal privacy and transparency in Sweden and I think in all countries, including Sweden, the EU, and the United States...that things have gone too far," she said during an interview with Sveriges Television (SVT).
When contacted by The Local for further comment, a spokeswoman for Ohlsson said all questions on the matter were now being referred to the Defence Ministry.
In a statement, Defence Minister Karin Enström of the Moderate Party said Sweden's intelligence exchange with other countries is "critical for our security" with rules that "balance security and privacy interests".
"Intelligence operations occur within a framework with clear legislation, with strict controls, and under parliamentary oversight," the statement read.
Via Twitter, Fredrik Federley of the Centre Party, who fought the passage of Sweden's controversial "FRA-law" that gives the agency the right to wiretap telephone and internet traffic that crosses Sweden's borders, said he wasn't surprised by the news.
BACKGROUND: Sweden passes divisive wiretapping law
"It's hard for me to be surprised by information about FRA/NSA cooperation. Been convinced the whole time that the point of FRA is to provide the USA more info," he wrote.
In subsequent exchanges with other followers, Federley said he had nothing against the exchange of "limited and relevant" intelligence between countries, but that he's against surveillance of a country's own citizens.
He added that if FRA is "running errands for the NSA" it should lead to a new debate about the agency's powers.
Meanwhile, Hans Linde, foreign policy spokesman for the Left Party said it was time for the government to "put all its cards on the table" with respect to how the Swedish and US intelligence agencies cooperate.
"Many European countries have protested against NSA's mass surveillance, but the Swedish government has been consistently silent. The question is whether we'll learn why Reinfeldt and Bildt haven't spoken about the NSA's mass surveillance," he said in a statement, adding the matter, if confirmed, would amount to a "huge scandal".
Ferm of the Green Party also demanded that the government come clean about how much they know about FRA and NSA cooperation.
"The government needs to tell us what's going on," she told The Local, adding she has requested Foreign Minister Carl Bildt and Justice Minister Beatrice Ask to come to parliament to answer questions on Sweden's intelligence operations.