This is stated in the report of the OSCE SMM to Ukraine.
The OSCE SMM also posted the video footage filmed with UAV on August 7 on its YouTube channel.
“At 22:15 on 7 August, an SMM long-range UAV spotted a convoy of eight canvas-covered six-wheeled cargo trucks (five KamAZ-4310 and the rest undetermined) travelling east along a road near Chystiakove (non-government-controlled, 62km east of Donetsk). Near Manych (non-government-controlled, 76km east of Donetsk), approximately 3.5km before reaching Ukraine’s border with the Russian Federation, the convoy turned east onto a dirt track that leads across the border,” reads the mission’s report.
The UAV then spotted a second convoy consisting of eight trucks and travelling westwards from the border with the Russian Federation along the same dirt track. The two convoys passed each other about five minutes after the second convoy entered Ukraine.
At around 23:25, the UAV spotted the first convoy exiting Ukraine via the same dirt track.
The OSCE SMM observed the convoy heading westward into Ukraine driving west and finally parking at the southern outskirts of Khrustalnyi (formerly Krasnyi Luch, non-government-controlled, 56km south-west of Luhansk) at 01:16 on 8 August.