Relatives of civilians killed when Nato aircraft bombed a Serbian town in 1999 have put their claims for compensation to a court in Germany, despite the fact that no German planes were involved in the action.
There are doubts about the military significance of Varvarin bridge
Ten civilians were killed when Nato jets targeted a bridge near a busy market place in the town of Varvarin, as part of efforts to put pressure on the then Serbian leader Slobodan Milosevic.
The relatives claimed a million euros in damages at the state court in Bonn.
They say Germany must take responsibility as a member of Nato.
Berlin has argued that it is not liable since neither German planes nor German pilots were involved.
Lawyers say a German court was chosen because the families have had support from human rights activists in Germany.
Some media in Germany have suggested that the country's foreign policy itself is on trial.
The suit could serve as a test case for others seeking damages from Nato countries.
The claimants scaled down their original request for 3.5 million euros when the proceedings opened, to bring it in line with other similar settlements in Germany.
Three people were killed and five injured in initial raids by F-16 fighters on the bridge in Varvarin, 110 miles (180km) south-east of Belgrade.
The aircraft returned minutes later, killing seven more and injuring another 12, among them people who were trying to help victims of the first attack.
Nato said that the bridge was a legitimate target and denied targeting civilians.
However, the claimants argue that the raid violated the Geneva Conventions, since it came without warning and was carried out on a busy market day.
"That was murder, bombing ordinary civilians in broad daylight," Zoran Milenkovic, whose 15-year-old daughter was killed in the raid, told the Associated Press news agency.
Doubts have also been raised about the military significance of the bridge, which has a maximum capacity of 12 metric tons.
Lawyers for the victims say the most important thing for the claimants is to get an admission of wrongdoing.
"The least important thing is the money, it's about someone saying that what happened was wrong," said lawyer Guel Pinar.