Eight people in the Swedish capital, Stockholm, were hospitalized with respiratory problems Friday after reporting an intense odor that police, who have opened an investigation, said may have been caused by a gas leak.

"Around 1:00 p.m. [1200 GMT] today, there were indications that there was a dangerous substance at [Swedish Security Services] SAPO's offices," said Patrik Soderberg, chief physician at the local health care authority Region Stockholm. 

"A total of eight people with symptoms have been treated at hospital," Region Stockholm said in a statement, adding that the "cause of the leak is still unclear."

Ambulances, emergency vehicles and police in gas masks were on hand as the building was evacuated.

Later, a large perimeter was cordoned off around the facility, with police citing "a potential gas leak."

The cordon was lifted some four hours later when it was determined that there was no leak and that those who had fallen ill were feeling better.

Sweden has been preoccupied with the potential ramifications of its decision to request NATO membership, facing threats from neighboring Russia over the move.

Sweden also considers itself a potential target for Islamist attacks as well after several highly provocative Quran burnings took place in the country while negotiations over NATO membership were ongoing with Turkey.

js/sms (AFP, Reuters)