STOCKHOLM (AP) — Traces of a toxic, colorless gas were found at the headquarters of Sweden’s security agency where a suspected gas leak last week forced authorities to evacuate some 500 people from the facility, a local paper reported Wednesday.

The daily Svenska Dagbladet newspaper said authorities had found traces of phosgene. The gas has a strong odor that can cause vomiting and breathing trouble and was used as a weapon in World War I.

There were no immediate comments from officials.

On Friday, eight people from the headquarters in Solna, just north of Stockholm, were hospitalized, following the evacuation. There were no reports of anyone being seriously injured.

Those admitted to the hospital suffered breathing problems, authorities said. Some of them were officers who smelled the gas when they arrived at the scene, police said.

Images showed first responders and police officers wearing gas masks at the security headquarters. Swedish media reported that a zone measuring 500 meters (about 547 yards) in diameter was set up protectively.

Authorities asked people living near the Swedish security agency, known by its acronym SAPO, to keep their windows closed at the time.

After the evacuation, SAPO said Friday that the rescue service “had established that there was no gas either inside the premises or outside the building.”