People linked with the U.S. Embassy in Stockholm have performed surveillance activities in Sweden without the knowledge of the host nation's authorities, a government officials said Saturday.

The surveillance has been going on since 2000, but Swedish authorities are still not aware of how widespread the practice was, said Justice Minister Beatrice Ask.

"It seems as though we haven't been fully informed and that's not good," Ask said.

Ask said it is not clear whether Swedish law has been violated, but that she expects U.S. authorities to cooperate with the Swedish investigation on the matter.

She did not disclose who were the targets of the surveillance operation carried out by people who had been "assigned by the embassy to undertake the measures."

Ask said the activities "seem to be similar" to those unveiled in Norway earlier this week, which included photographing and gathering information about individuals for surveillance and security purposes. That information was then sent to the United States.

"We welcome that those countries that have a heightened threat risk apply their own measures to reduce the risk for attacks, but of course it has to be done in line of what the Swedish law says and permits," she said.

The Foreign ministry summoned the U.S. Ambassador to Sweden, Matthew Barzun, on Saturday in connection with the surveillance program, said Teo Zetterman, the ministry spokesman.

U.S. Embassy staff in Stockholm were not immediately available to comment on the matter.

Earlier this week, Norwegian media reported that the U.S. had systematically monitored Norwegian residents deemed potential security risks to the U.S. for the past 10 years. Similar to the case in Sweden, Norwegian government officials said they had not been informed about it.