Turkish warplanes mistakenly killed 35 smugglers and other villagers in an operation targeting Kurdish rebels in neighboring Iraq, a senior official said.
It was among the largest one-day civilian death tolls during Turkey's 27-year drive against the guerrillas.
The killings spurred angry demonstrations in Istanbul on Thursday and several cities in the mostly Kurdish southeast.
Huseyin Celik, a spokesman for Prime Minister Recep Tayyip Erdogan's ruling party, said authorities were still trying to identify the dead, but that most were youngsters from an extended family in the mostly Kurdish-populated area that borders Iraq.
All of the victims were under 30, and some were the sons of village guards who have aided Turkish troops in their fight against rebels, he said.
"According to the initial information, these people were not terrorists but were engaged in smuggling," Celik said, adding that Turkey was ready to compensate the victims.
"If there was a mistake, if there was a fault, this will not be covered up, and whatever is necessary will be done."
In Istanbul, police used tear gas and water canons to disperse pro-Kurdish protesters denouncing the air strikes, the Dogan news agency reported.
Earlier, the Turkish military confirmed the Wednesday night raids, saying its jets struck an area of northern Iraq frequently used by rebels to enter Turkey after drones detected a group approaching the often unmarked mountainous border. Border troops were on alert following intelligence indicating that Kurdish rebels were preparing attacks in retaliation for recent military assaults on the guerrillas.
The military said it conducted strikes in areas where the rebels have bases far away from civilian settlements.
Pro-Kurdish legislator Nazmi Gur said earlier that most of those killed were teenagers making a living out of smuggling cigarettes from Iraq into Turkey and claimed that officials should have known that Turkish smugglers would be operating in the area.
Video footage provided by Dogan on Thursday morning showed mourners, some crying, as they surrounded more than a dozen bodies that lay side-by-side and wrapped in blankets in the Turkish village of Ortasu.
Ahmet Deniz, a spokesman for the rebel group, said earlier that the victims were among a group of about 50 people attacked on their way back to Turkey from Iraq's self-ruled northern Kurdish region.
Most of the survivors were injured, he said.
"Those who were killed yesterday had no links to the PKK. They were only smugglers who were on their way back to Turkey from Iraq," Deniz said, referring to the Kurdish rebel group, the Kurdistan Workers' Party.