It would be "an historic mistake" for Russia to send its forces over Ukraine's eastern border, Nato's secretary general has warned.
Anders Fogh Rasmussen also told ITV News Europe Editor James Mates that the military alliance would do all it could to protect members if they are attacked by Russia.
NATO Sec Gen @andersfoghr Rasmussen confirms to me the alliance will take all steps to defend any member attacked by Russia, including war.
Rasmussen: "Our guarantee to our members is steadfast". But: "we can't continue to disarm while Rus increases its def spending". #NATO
An unusually frank Nato Secretary General issued an unequivocal warning on the course of events should Russia attack Latvia or Estonia.
The West responds with sanctions and closer political ties with Ukraine as Russia's President seals the annexing of Crimea to much fanfare.
Supporters of the controversial fracking industry believe shale gas could be America's most potent weapon in the stand-off with Russia.