A letter bomb has exploded at an office of the Swiss nuclear power industry in the northern town of Olten, injuring two people, say canton Solothurn police.
The explosion happened as staff were opening the morning's post in the office of swissnuclear, according to spokeswoman Thalia Schweizer.
swissnuclear is a lobby group representing the national power companies Axpo, Alpiq and BKW.
Schweizer said the two staff members had been taken to a hospital but their injuries appeared to be superficial. It is not yet known who was behind the attack or any apparent motive.
Switzerland currently has five nuclear reactors in operation at four power stations. However, nuclear power has been a source of great debate since the accident at the Fukushima plant in Japan.
Energy Minister Doris Leuthard decided to suspend all current requests to build replacement nuclear power stations in Switzerland earlier this month.
Environmental campaigners have condemned the attack. The Green party said it, “had absolutely nothing to do with the anti-nuclear movement in Switzerland or abroad”, while Greenpeace, which held a demonstration in Olten on Thursday, said its actions were based on non-violent principles.
swissinfo.ch and agencies