Ukraine must keep close ties with Europe to prevent Russia using energy as a "new nuclear weapon", interim Prime Minister Arseniy Yatsenyuk has warned.
Mr Yatsenyuk was speaking after signing an association agreement with the EU ensuring closer political ties.
He also wants the EU to provide Ukraine with natural gas to counter likely increases in the cost of supplies from Russia.
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.