Two Russians captured by Ukrainian forces during a firefight in the ex-Soviet state's separatist east have both admitted to serving in the Kremlin's armed forces, the OSCE said on Thursday.

"Both individuals claimed that they were members of a unit of the Armed Forces of the Russian Federation. They claimed that they were on a reconnaissance mission. They were armed but had no orders to attack," the Organization for Security and Co-operation in Europe reported after conducting interviews with the two wounded men in a Kiev hospital.