At least eight migrants drowned and more were missing when their boat capsized early on Thursday while attempting to cross the Drina river from Serbia to Bosnia and Herzegovina, the chief of the Bosnian rescue team said.
Vlada Rankic, the leader of the civil defence rescue team, told reporters a boat had overturned at around 06:00 a.m. (04:00 GMT) during an illegal border crossing.
"We don't have precise information, eight bodies have been retrieved until now," Rankic told reporters, speaking near the site of the accident close to the Bosnian town of Bratunac.
He added that rescuers were searching for a mother and a baby. "Unfortunately, we don't think there will be survivors."
He said civil defence rescue teams, Bosnian and Serbian border police, divers and firefighters were deployed in search along the forested river banks.
"We deployed all possible resources," he said.
Rankic could not say how many people were on the boat. Earlier, Civilian Defence director Boris Trninic told the Srna news agency that unofficial estimates put the number at 30, of which 15 reached the shore.
N1 television reported that rescuers were also searching for a smuggler who took the migrants across the river.
Bosnian authorities could not immediately be reached for comment. The border police confirmed the incident took place early in the morning, without providing detail.
Serbian officials confirmed that an incident had taken place on the river, but could not confirm the deaths. Interior Minister Ivica Dacic said 25 people were on board, of whom only 18 reached the Bosnian side.
Thousands of people from the Middle East, Afghanistan, Pakistan and North Africa annually use the so-called Balkan route, which runs via Turkey, Bulgaria, North Macedonia and Serbia, to reach wealthy Western countries.
Many migrants are crossing borders with the help of elaborate networks of smugglers and accidents are frequent.