Russian combat forces are seen engaging in military operations inside Ukraine in the latest satellite imagery released by the Nato's Allied Command Operations.
Captured by DigitalGlobe in late August, the imagery shows Russian self-propelled artillery units moving in a convoy through the Ukrainian countryside and then preparing for action by establishing firing positions in the area of Krasnodon.
Nato Allied Command Operations Comprehensive Crisis and Operations Management Centre (CCOMC) director Dutch brigadier general Nico Tak said: "Over the past two weeks we have noted a significant escalation in both the level and sophistication of Russia's military interference in Ukraine.
"The satellite images released today provide additional evidence that Russian combat soldiers, equipped with sophisticated heavy weaponry, are operating inside Ukraine's sovereign territory.
"We have also detected large quantities of advanced weapons, including air defence systems, artillery, tanks and armoured personnel carriers being transferred to separatist forces in Eastern Ukraine.
"The presence of these weapons along with substantial numbers of Russian combat troops inside Ukraine makes the situation increasingly grave."
Other surveillance photos depict substantial activity inside Russia in areas adjacent to the border with Ukraine, which Nato believes is being conducted in direct support to forces operating inside Kiev.
Tak said: "Russia is reinforcing and resupplying separatist forces in a blatant attempt to change the momentum of the fighting, which is currently favouring the Ukrainian military.
"Russia's ultimate aim is to alleviate pressure on separatist fighters in order to prolong this conflict indefinitely, which would result in further tragedy for the people of Eastern Ukraine."
The pro-Russian rebels are reportedly advancing on the Ukrainian security forces in both Luhansk and Donetsk, and also around Mariupol, over the last few days.
The anti-government forces also attacked a Ukrainian navy vessel in the Azov Sea by artillery in the first incident of the type at sea since the start of the crisis in April.
Having consistently denied troops deployment in Ukraine, Russian President Vladimir Putin has reportedly called for immediate talks on 'statehood' for southern and eastern Ukraine.
In a televised statement Putin said: "We need to immediately begin substantive talks... on questions of the political organisation of society and statehood in south-eastern Ukraine with the goal of protecting the lawful interests of the people who live there."
Image: The new Nato imagery provide additional evidence that Russian combat soldiers are operating inside Ukraine. Photo: courtesy of Nato.