Downing Street has warned that Russian President Vladimir Putin’s plan for invading Ukraine has effectively “already begun”.
Number 10 suggested that Russia’s “playbook” for launching military action against its neighbour had begun to “play out in real time”.
But a “window for diplomacy” still remains to prevent war in Europe, Downing Street added.
Earlier on Monday, Foreign Secretary Liz Truss held talks with NATO secretary general Jens Stoltenberg in Brussels about the continuing crisis.
After their meeting, Ms Truss warned that a Russian invasion of Ukraine “looks highly likely” and that the UK and NATO allies were “stepping up preparations for the worst case scenario”.
Asked about Ms Truss’s comments at a regular briefing for reporters later, the prime minister’s official spokesman said: “That is our assessment.
“The intelligence we’re seeing suggests Russia intends to launch an invasion and that President Putin’s plan has already begun, in effect.
“We’re seeing elements of the Russian playbook that we would expect to see in those certain situations start to play out in real time.
“We’ve been working with NATO allies to call that out when we see it.
“The intelligence we have suggests that they still intend to launch an invasion and we stand ready to act as needed.
“But, crucially, we still think there is a window for diplomacy – as we’ve seen with discussions over the weekend – and we want to explore those.”