A parcel bomb exploded on Thursday in northern Switzerland, injuring two people at an office of Swissnuclear, the federation of nuclear power companies, DPA reported.
Initial reports had incorrectly indicated the blast was at UBS bank, which has an office in the same building, though officials confirmed later that the financial firm was not affected. The area is surrounded by police.
The explosion occurred just after 8am (0600 GMT) in the city of Olten, in the canton of Solothurn, according to the news website 20 Minuten.
Cantonal police said there was no immediate claim of responsibility.
The injured people face no direct threat to their lives, but further information on their condition was not immediately available.
Swissnuclear operates four nuclear power plants, according to its website, which together provide about 40 per cent of the country's electricity.
Nuclear power has come under close scrutiny in Switzerland since an earthquake earlier this month damaged a reactor in Japan. Shortly after the accident, the federal government announced it was suspending approvals for new nuclear plants.