Russia says it has deployed forces to monitor so-called de-escalation zones in southern Syria.
The defence ministry said military police had been sent to Eastern Ghouta on the edge of the capital Damascus, and to an area in the south-west.
It is the first time foreign personnel have been despatched to help implement the "safe zones" agreed with Turkey and Iran earlier this year.
Rebel groups have not publicly signed up to the de-escalation agreement.
A Russian defence ministry spokesman, Lt Gen Sergei Rudskoi, said a contingent had set up two checkpoints and 10 observation posts on front lines between Syrian forces and rebels in the two areas.
He said Israel, which borders Syria's south-west, had been informed in advance. Israel is reported to have opposed the idea of Russia policing the zones, fearing it would be used as cover by Hezbollah militants and other Iranian-backed militia to move closer to Israel's front line.
A plan for four de-escalation zones was agreed between Russia and Iran, both of whom strongly support Syria, and Turkey, which backs the rebels, at talks in the Kazakh capital, Astana, in May.
The plan excludes attacks on militants from so-called Islamic State (IS).
Lt Gen Rudskoi said military police had been sent to checkpoints and monitoring posts in Eastern Ghouta, in parts of which the Syrian military declared a halt to fighting on Saturday following talks in Egypt between Russia and "moderate" rebel groups.
However, the UK-based monitoring group, the Syrian Observatory for Human Rights, said Syrian aircraft have carried out air strikes there since then.
Syria's war has claimed more than 330,000 lives since it erupted in 2011, with millions more displaced.