Britain's Chief of the Defence Staff Tony Radakin on Wednesday urged the international community to remain united against what he called Russian President Vladimir Putin's "deeply irresponsible" nuclear rhetoric.
"He (Putin) has few options left. Hence, the nuclear rhetoric," he said during a speech.
"And while this is worrying and deeply irresponsible, it is a sign of weakness, which is precisely why the international community needs to remain strong and united."
British defence minister Ben Wallace met his U.S counterpart in Washington this week to discuss shared security concerns about the situation in Ukraine.
Asked during a question and answer session following his speech how likely he thought it was that Putin was preparing to launch a nuclear strike in Ukraine, Radakin declined to answer directly.
"I don't think you'll be surprised for me to duck giving you a precise likelihood of where Russia is," he said.
"I would just stress the recklessness of Russia using that language around nuclear and that this is a desperate ... We need to focus on our continued support to Ukraine and not be drawn to reckless rhetoric."
(Reporting by Kylie MacLellan, writing by Muvija M)