Turkish Prime Minister Binali Yildirim said two military personnel were killed when a helicopter was downed during Ankara's offensive against a Kurdish militia in northern Syria.
"At this stage, we can say that one out of two helicopters was downed. We have two martyrs," Yildirim said in televised remarks, but added that there was: "no evidence (yet) in our hands to prove that it was a result of outside intervention."
On January 20, Turkey launched a military operation against the Kurdish People's Protection Units (YPG) militia in its western enclave of Afrin, backing Syrian rebels with air strikes and ground troops.
Ankara says the YPG is a "terrorist" offshoot of the outlawed Kurdistan Workers' Party (PKK), which has waged a three-decade insurgency inside Turkey and is blacklisted by Washington and the European Union.
Yildirim said the helicopter was on a mission in the Afrin region as part of Ankara's offensive dubbed Operation "Olive Branch".
Mustefa Bali, spokesman for the US-backed Syrian Democratic Forces dominated by the YPG, said on Twitter that a helicopter had been hit in the Rajo area of northwest Afrin, near the Turkish border.
But the state-run news agency Anadolu said the incident happened in the southern border province of Hatay, with private run Dogan news agency saying authorities were trying to reach the wreckage in the Kirikhan district.
Earlier, Erdogan said a helicopter had been shot down without saying who was responsible, admitting that such incidents were expected in times of conflict.
"Of course, these kinds of things will happen. We are in a war. We will have losses, but we will cause the other side to have losses as well," he said in a televised speech, vowing to make the perpetrators pay "a much heavier price."
- 'Threat to Turkey' -
Despite the officials' comments, the Turkish military said one of its helicopters crashed at 1300 (1000 GMT) killing two military personnel but did not give a reason for the incident, only saying that a technical investigation had begun in a statement.
On Friday, the military said one soldier was killed during clashes with the YPG in the Afrin region.
Last Saturday, seven Turkish troops died in the worst single-day loss of the operation so far, with five killed in a tank attack.
Some 1,141 "terrorists" had been neutralised during the operation, Erdogan said, referring to those killed but also those captured or wounded.
It was not immediately possible to verify this figure.
Yildirim earlier said Turkey had not launched its operation in Afrin to enter into a war or because it had "an eye" on another country's territory.
"Excuse me but no state would ignore a terror organisation growing like a tumour next to it," he said during a televised speech in the western province of Mugla.
"This is a threat to Turkey which Ankara has the natural right to fight under international and domestic law," Yildirim added.