The United States for the first time Tuesday held Russia responsible for the deaths of dozens of Turkish troops in Syria as it vowed accountability.
An airstrike last month in the Idlib region killed 34 Turkish soldiers, although Ankara blamed Syrian President Bashar al-Assad and reached a new ceasefire deal with Moscow.
Secretary of State Mike Pompeo, announcing new sanctions on Syrian officials, placed blame on Russia, which along with Iran has backed Assad in his bloody quest to crush rebels.
"We believe Russia has killed dozens of Turkish military personnel in the course of their military operation," Pompeo told reporters, without naming a specific incident.
"We stand with our NATO ally Turkey and will consider additional measures that support Turkey at the end of the violence," he said.
Analysts widely doubted that Assad's rundown air force could effectively hit Turkish forces but until now the United States had steered clear of blaming Russia, mindful of official statements by Ankara.
After the killings, Turkey killed dozens of Syrian government troops as retaliation but President Recep Tayyip Erdogan flew to Moscow to negotiate a ceasefire with his counterpart Vladimir Putin that includes joint Russian-Turkish patrols.
Idlib has been the last major battleground between Assad's forces against jihadists and their rebel allies, who are backed by Turkey.
The offensive launched in December caused a new humanitarian crisis in Syria's brutal nine-year civil war with close to one million people fleeing in the dead of winter.
Pompeo announced new sanctions against Syrian Defense Minister Ali Ayoub, accusing him of destroying an earlier truce through the offensive.
"His deliberate actions since December 2019 have prevented a ceasefire from taking hold inside Syria," Pompeo said.
Under the sanctions, any US assets of Ayoub are frozen and the United States can prosecute anyone for financial transactions with him.
US officials had earlier pointed to the deaths of Turkish troops as proof that Ankara should be cautious about building relations with Russia.
Turkey has defied warnings from its NATO alliance and was kicked out of the US F-35 program after it went ahead and bought the S-400 missile defense system from Russia, although it has not activated it.
© 2020 AFP