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.
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."