Russian defence officials say they are getting closer to a deal with the US on air safety in Syria, after aircraft from both countries flew within miles of each other last weekend.
The US Pentagon said "progress was made" in the third round of such talks.
Russian and US combat aircraft were in visual contact with each other, 10 to 20 miles (15-30km) apart, on Saturday.
Russian began air strikes in Syria on 30 September, saying it was targeting Islamic State (IS) militants.
But Western countries and Syrian activists say Russian planes have been hitting non-IS targets - a claim Moscow denies.