Nato's decision to release over 20 satellite images and associated maps of the Russian military build-up on Ukraine's eastern frontier is a signal of the concern among the alliance's commanders that a Russian military option against Ukraine is very much on the table, the BBC's diplomatic correspondent Jonathan Marcus reports.
The imagery issued by Nato's Supreme Headquarters Allied Powers Europe (Shape) reportedly dates from late March and early April. It encompasses five locations in an arc around Ukraine's frontier. Imagery from a sixth site was provided by Airbus Defence and Space.
The images show:
- sophisticated warplanes, and helicopters
- an airborne early warning aircraft (similar to the Nato Airborne Early Warning and Control Aircraft, or Awacs)
- a number of military deployments on the ground
2. Buturlinovka Air Base
Among the most interesting of these is what is thought to be an airborne or Spetznaz (Special Forces) brigade at the Yeysk air base on the Sea of Azov some 20km (12 miles) from Ukrainian air space.
At a number of other locations the massed vehicles of mechanised infantry or motor rifle brigades can be seen - not just tanks and infantry combat vehicles but artillery and the large number of supply trucks needed to keep a mechanised force on the move.
Before and after
An unnamed Russian military official responded to the release of the images by saying that the satellite photos were actually taken in 2013.
Nato, however, rejects the Russian allegations out of hand.
It says: "The dates of the images released by Shape were collected by the Digital Globe satellite 'Constellation' between late March and early April 2014. The images are unclassified and are commercially available in Digital Globe's public archive. Shape did not alter or edit the images in any way prior to release."
On Thursday Nato released additional images obtained from Digital Globe which show the same locations in 2013 and early 2014 when, Nato says, there was "no evidence of any military activity at all".
A senior Nato spokesman says that when reviewed alongside images released by Shape earlier on Thursday, "it is clear that the military build-up of forces occurred in early March 2014".
He says that Nato "stands firm in its assessment that Russian forces in the vicinity of the border with Ukraine number in the range of 35,000 to 40,000 troops and are equipped with infantry fighting vehicles, tanks, combat aircraft, logistics, and artillery".
- This 14 March 2014 photo (provided by Airbus Defence and Space) of the Primorsko-Akhtarsk airbase in south-western Russia shows a build-up in the number of tactical aircraft
- There are primarily Sukhoi Su-25 Frogfoot strike aircraft (lower left) and Sukhoi Su-27 (on the right)
- While possibly deployed to initially be available over Crimea, they are also within range of a lot of eastern Ukraine and represent a threat to any Ukrainian armoured units