Jake Sullivan, the White House national security adviser, spoke on the attack close to the border with Poland:
"If there is a military attack on Nato territory, it would ... bring the full force of the Nato alliance to bear in responding to it,"
The UK's Michael Gove on the same, warned that Putin was "pushing the boundaries", and has "no moral limits".
The base targetteed is in Yavoriv, called the International Centre for Peacekeeping and Security and previously used by Nato troops to train Ukrainian soldiers.
- no Nato troops were at the site at the time of the attack
- Russia said it had killed "up to 180" foreign fighters & destroyed a cache of weapons donated by the West in the long-range missile attack