MUNICH (Reuters) - Supplying weapons to Ukraine, an option under consideration in Washington, would escalate the conflict, British Defense Secretary Michael Fallon said on Friday.

Britain backed a new effort by the leaders of Germany and France to try to halt the Ukraine conflict, Fallon told Reuters in an interview during the Munich Security Conference.

But he said that territory taken by Ukrainian separatists since the Minsk agreement in September should "absolutely not" be recognized in any new ceasefire.

Fallon voiced concern that Russian military planners may have "lowered the threshold" for the use of nuclear weapons and said Britain must update its own nuclear deterrent in response to Russian modernization of its nuclear forces.

(Reporting by Adrian Croft; editing by Stephen Brown)