Turkish President Recep Tayyip Erdogan has warned Russia to "get out of our way" in northern Syria as his forces fight President Bashar Al-Assad's regime.
The warning came after 33 Turkish soldiers were killed by airstrikes in northern Idlib province on Thursday - the highest number in a single day since Turkey first intervened in Syria in 2016.
Ankara has accused Russia warplanes of carrying out the strikes but Moscow has blamed the Syrian military.
The development has raised the prospect of an all-out war with millions of Syrian civilians trapped in the middle.
Syrian government forces have been on a weeks-long offensive in Idlib province, the country's last rebel stronghold, which borders Turkey.
Thousands of Turkish soldiers are deployed inside rebel-controlled areas of Idlib province, which is dominated by al-Qaida-linked militants.
The Idlib offensive has pushed nearly 950,000 displaced civilians toward the Syrian-Turkish border amid cold winter weather.
Late on Friday Turkey's Defence Ministry said another of its soldiers was killed and two were injured, this time by Syrian government shelling.
The announcement also said Turkish forces hit Syrian government targets and a number of Syrian troops were "neutralised".
Erdogan had given the Syrian government until the end of the month to pull back from areas captured in Idlib, threatening large-scale military action if they didn't.
But any large scale Turkish military action risks more loss of life among Turkish soldiers, and it's not clear what Erdogan might do. He has kept unusually silent since the 33 deaths.
Turkey began reinforcing its forces in Idlib earlier this month in a bid to thwart the Syrian government offensive, which began in early December.
NATO envoys held emergency talks Friday at the request of Turkey, a NATO member. While urging de-escalation in Idlib, NATO offered no further assistance.
Erdogan and Russian President Vladimir Putin spoke by telephone on Friday and discussed implementing agreements in Idlib, the Kremlin said. Fahrettin Altun, Erdogan's director of communications, said they had agreed to meet "as soon as possible."
Erdogan also spoke with other world leaders, including President Donald Trump and German Chancellor Angela Merkel.
UN Secretary-General Antonio Guterres called for an immediate cease-fire in Idlib. He warned that "without urgent action, the risk of even greater escalation grows by the hour, and as always, civilians are paying the gravest price.''