"The EU (European Union) relies on Russia for over 40% of its gas, and with some countries Russia has a complete monopoly of supply. If Russia gets its way, Europe will be increasingly hooked on its gas," Truss told the Chatham House think tank.

"We have to end this strategic dependency," she said, adding she would meet her Ukrainian counterpart on Wednesday to strengthen their ties and repeat the message that any Russian incursion into Ukraine would be a mistake.

(Reporting by William James, writing by Elizabeth Piper, Editing by Kylie MacLellan)