It was discovered by the Swedish intelligence service Säpo in 2009, as two people were found to also be tracking the suspected terrorists that Säpo was following. Sweden protested to the CIA, and the American agents left the country shortly after.
The newspaper draws parallels to Washington's failure to inform Pakistan before it tracked and killed Osama bin Laden three weeks ago, and says that also Sweden "has become the scene of a foreign power's terror hunt without the knowledge of the Swedish government".
The news agency TT have asked Foreign Minister Carl Bildt and Justice Minister Beatrice Ask for a comment on Sunday evening, but they declined.
"You're not supposed to do it, but I wouldn't say it's unique. Even friends spy on each other," Dennis Töllborg, law professor at the Gothenburg Research Institute, tells Radio Sweden.
"The real danger in this is did the Swedish government allow it? Because they cannot allow it. If they allow it, then they leave part of Swedish sovereignity to another country. That's very serious," says Töllborg.
And, Töllborg says, if the government did not know but Säpo did, that would also be very serious.
"Säpo does not have the mandate to allow foreign intelligence to do these things. [If Säpo allowed this], then, Säpo is not under control by the authorities. That's also very dangerous. This is the only story that is acceptable, which is coming out now," says Töllborg.