Serbia's war-crimes prosecutor's office says five former policemen are under investigation in the killing of non-Serbs in Croatia in 1991.
The prosecutor's office says they are suspected of killing at least six civilians and engaging in intimidation, terror and torture. It says, without providing details, that the killing took place in eastern Croatia during the Serb-Croat war in 1991.
Thursday's statement added that four suspects have been detained while one remains at large.
The pro-Western government formally applied for EU membership this week and appears to be trying to show its resolve to prosecute war crimes.
The prosecutor's office says the case was taken over from Croatia, where some 10,000 people died in the war.