Police in the Ukrainian city of Odesa have launched an investigation into the disappearance of the lawyer of a Russian citizen who is on trial for allegedly fighting alongside separatists in Ukraine's east.

Yuriy Hrabovskiy, who stayed in a local hotel, went missing on March 5.

Hrabovskiy's client, Aleksandr Aleksandrov, and another Russian citizen, Yevgeny Yerofeyev, were detained in Ukraine's eastern Luhansk region in May 2015 and later charged with terrorism.

The two men first admitted in a video that they were on active duty with the Russian military in eastern Ukraine when they were captured, but later retracted that.

Moscow contends Yerofeyev and Aleksandrov were not serving in the country's armed forces when they were detained by Ukrainian forces.

On March 9, a court in Kyiv was forced to reschedule Aleksandrov's trial to March 15 due to Hrabovskiy's absence.

Based on reporting by UNIAN and Interfax