Britain released photographs on Wednesday of what it described as Russia's most advanced anti-aircraft artillery system, being operated in eastern Ukraine, saying it was further proof of Russia's military involvement in the conflict.

The Foreign Office released an "infographic" giving details of the truck-mounted SA-22 surface-to-air missile system and photographs published by media and a defence consultancy said to show it operating in eastern Ukraine within the last few weeks.

"The presence of the SA-22 in eastern Ukraine is yet more proof of direct Russian military involvement in the conflict," the British ambassador to NATO, Adam Thomson, said in releasing the pictures via Twitter.

"We call on Russia to fully implement its Minsk commitments," he said, referring to a truce agreement that calls for withdrawal of foreign forces from Ukraine.

The British slide is headed "How to recognise Russia's Pantsir-S1 (or SA-22) which is not operated by Ukrainian forces."

Russia has denied repeated Western accusations that it has sent soldiers and large amounts of heavy weaponry to eastern Ukraine.

NATO Secretary-General Jens Stoltenberg said on Wednesday that "Russian forces, artillery and air defence units as well as command and control elements are still active in Ukraine."