The United States believes Russia has killed dozens of Turkish military personnel in the course of its military operations in Syria, US Secretary of State Mike Pompeo said, saying that Washington continued to offer support to its Nato ally Turkey.
Speaking at a news conference at the State Department, Mr Pompeo did not specify where or during which incident the Turkish soldiers were killed.
It was the first time Washington has directly pointed its finger at Moscow over the death of Turkish soldiers.
"We believe Russia has killed dozens of Turkish military personnel in the course of their military operations, and we stand with our Nato ally Turkey and we continue to consider additional measures to support Turkey and to end the violence in Idlib and in Syria more broadly," he said.
Last month, an air strike that Ankara said was carried out by the Syrian government forces killed at least 34 Turkish soldiers, the deadliest attack on the Turkish army in nearly 30 years.
The attack came after Russia-backed Syrian government forces had intensified their campaign to retake Idlib, the last rebel-held stronghold in the country. That prompted Turkey, which backs some rebels looking to oust Syrian President Bashar al-Assad, to mount a counter-offensive to repel their advances.
Turkey and Russia, which back opposing sides in Syria's war, agreed on March 5 to halt hostilities in the country's north-west after a recent escalation of violence displaced nearly a million people and brought the two sides close to confrontation. The ceasefire has largely held since then.