"Today at 7 a.m. (0400 GMT) an unknown plane carried out a bombing attack on Snizhne. The flight can be described only as a cynical provocation," Lysenko, a spokesman for Ukraine's National Defense and Security Council, told reporters.

His remarks appeared to be an accusation against Russia, since the rebels have not used aircraft in the conflict.

Kiev's fresh charges follow its accusation on Tuesday that the rocket that downed the An-26 may have been fired from Russian territory.

Foreign ministry spokesman Vasyl Zvarich, also suggesting Russian involvement in the Snizhne attack, said Ukraine hoped the EU's threats to move to a tougher level of sanctions against Russia were not simply "declaratory".

The EU last Saturday targeted Ukrainian separatist leaders with travel bans and asset freezes on Saturday, avoiding fresh sanctions on Russian business to avoid antagonizing Moscow, its main energy supplier.

Saying Ukraine had proof of Russian participation in the activities of the rebel fighters, Zvarich said: "We hope that a resolution will be taken which will give an objective evaluation of Russia's actions in Ukraine's eastern regions and will also condemn Russia's support for terrorist and separatist groups."

In other fighting in the three-and-a-half month conflict with separatists in the Russian-speaking east of Ukraine, government forces said they had lost another six soldiers in attacks on their positions near the border with Russia.

In all, since the start of the government's "anti-terrorist" operations in mid-April, a total of 258 Ukrainian servicemen have been killed, 922 injured and 45 are captive, military spokesman Andriy Lysenko said.

Hundreds of civilians and rebels have also died. (rt/ez)