Nato has failed to find Bosnian Serb fugitive Radovan Karadzic in a raid on his old stronghold.
S-For has intensified its search for Karadzic
A priest and his son were injured in the operation in the Bosnian mountain town of Pale by around 40 troops from the US, Britain and other countries.
Mr Karadzic, who has been on the run for around seven years, is wanted on charges of genocide during the 1992-95 war.
"We conducted a focused international operation in Pale... we did not find him," said Nato Captain Dave Sullivan.
The BBC's Nick Hawton in Belgrade said the troops surrounded a church and a priest's house in the town of Pale, near the Bosnian capital Sarajevo, in the early hours of Thursday.
They used explosives to break into the building, shattering windows and leaving a hole at the main entrance.
Serbian Orthodox priest Jeremia Starovlah and his son Aleksandar were wounded in the blast.
They were evacuated by military helicopter to a civilian hospital in the northern town of Tuzla.
A hospital spokeswoman said both had suffered heavy injuries to the head and the priest was on a life support machine.
"Their lives are still in danger," said spokeswoman Amra Odobasic.
The priest's wife told Bosnian Serb radio the raid was like "the worst horror movie".
"We were awoken by shooting," Vitorka Starovlah said. "Soldiers burst into the house and immediately took them to another room... a soldier put a gun to my head. I heard my husband cry for help, but I could do nothing."
Karadzic has been on the run since the end of the war
Eyewitnesses reported hearing gun fire as troops sealed off the centre of town, but this was not confirmed by Nato peacekeepers.
S-For has intensified its search for Mr Karadzic and his supporters before it hands over its mission to a European Union force by the end of this year.
Our correspondent says Nato will not officially describe the latest raid as a failure - a spokesman said information from such operations is always valuable.
But this is the second time in three months that Nato has mounted an operation in Pale in its hunt for Mr Karadzic, without finding the fugitive.
In a major operation in January, troops targeted the same church without success after a tip-off that he had returned to his former stronghold to seek medical attention.
Mr Karadzic's wife, who still lives in the town, told the BBC in March that she had not seen her husband for four years and did not know where he was.