Turkey experienced its bloodiest day yet during its three-week offensive in the Syrian-Kurdish enclave Afrin, as 11 soldiers were killed in several incidents, according to military statements.
Among the dead were two soldiers killed on Saturday when a helicopter went down.
The military did not give an exact reason for the helicopter's crash, only saying investigations by a technical committee were ongoing.
"We do not have clear evidence as to whether it fell due to an external intervention," Prime Minister Binali Yildirim told reporters in the Aegean province of Mugla.
President Recep Tayyip Erdogan, who first announced the incident, had indicated at the time that the helicopters may have been downed.
Erdogan, speaking to members of his ruling Justice and Development Party (AKP) in Istanbul, also said earlier on Saturday: "We might lose a helicopter, but they will pay a heavy price for this."
The military announced additional deaths in three separate statements throughout the day, without specifying the circumstances.
Eleven soldiers were also injured.
The deadly day came as Turkish operations just across the Syrian border in Afrin are entering their fourth week, as Ankara battles the Kurdish People's Protection Units (YPG), advancing on several different fronts into the territory.
Ankara considers the YPG - the main Western ally in the fight against the Islamic State extremist group in Syria - a terrorist organisation because of its ties to a Kurdish insurgency in Turkey.
A spokesman for the YPG in Afrin, Mustafa Bali, claimed his fighters had downed the helicopter. This would mark the first time the YPG have downed a Turkish aircraft in the Afrin offensive.
The YPG released a video that they alleged showed the helicopter being downed. dpa could not independently verify the content.
Turkey has lost 30 soldiers in the operation in Afrin, according to data compiled from the military statements. The military says it has "neutralised" more than 1,100 "terrorists" in Afrin.
The YPG has self-reported at least 70 deaths among its own ranks.
The Syrian Observatory for Human Rights, a monitoring group, says at least 68 civilians have been killed. Turkey insists it does not target civilians and says none have been killed as a result of its military's actions.