Russia has not taken its “foot off the gas” for a possible invasion of Ukraine which could happen within hours, Defence Secretary Ben Wallace said on Wednesday.
He urged Vladimir Putin to build up trust - not troops - to defuse the crisis.
The Russian president said on Tuesday that a decision had been taken for a partial withdrawal of some of the 130,000 Russian forces estimated to be surrounding Ukraine, with the Defence Ministry in Moscow saying this had already begun.
However, US president Joe Biden, and western sources, have cast doubt on whether the Kremlin is pulling back troops, warning that an invasion may still happen.
Speaking on Sky News on Wednesday morning, ahead of a meeting of Nato defence minister in Brussels, Mr Wallace said: “The latest intelligence is that there over 100 battalion tactical groups of the Russian ground forces, that is 60 per cent of the entire Russian land combat power on the borders of Ukraine, 130,000 plus troops...but also out at sea there is effectively a significant flotilla of Russian amphibious landing ships and indeed war ships and missile ships.
“They have not taken the foot off the gas.
“Readiness is one of the first signs you always get about how serious a country is.
“If you wanted to inflict intimidation on Ukraine, that deployment is doing exactly that.”
He added: “It’s a very significant force, it’s a force that would overwhelm Ukraine should it be deployed.
“That is why we need to see clear de-escalation by the removal of troops at the same time as enter into discussion with Russia.”
He emphasised that the West had not seen evidence of withdrawal, as claimed by Moscow.
