Turkey's military has denied that it mistakenly told Russian warplanes to bomb a building in Syria on Thursday, killing three Turkish soldiers.
Kremlin spokesman Dmitry Peskov told reporters the pilots were "guided by co-ordinates" from "Turkish partners".
"There should not have been Turkish troops at those co-ordinates," he said.
But the Turkish military insisted the troops had been at the building for 10 days and that Russia had been advised of their position on Wednesday.
The two countries, which support opposing sides in Syria's almost six-year civil war, are working together to drive the Islamic State group from its last stronghold in Aleppo province.
Turkish-backed rebel fighters have been besieging al-Bab from the north since December, while Russian-backed government forces are advancing from the so