The Prime Minister has said the West should not listen to Vladimir Putin's "sabre-rattling" and "bogus threats".
Liz Truss was asked how the West should respond to the Russian president’s partial military mobilisation and warnings his country would use "all the means at our disposal" to protect itself.
She told CNN's State Of The Union programme: "We should not be listening to his sabre-rattling and his bogus threats.
"Instead, what we need to do is continue to put sanctions on Russia and continue to support the Ukrainians because if Putin is allowed to succeed, this wouldn't just send a terrible message in Europe and of course, huge threats to the Ukrainian population themselves, but it also would send a message to other authoritarian regimes around the world that it's somehow acceptable to… invade a sovereign nation.
"So this is why it's so important that we continue to be resolute, we don't listen to the sabre-rattling that we're hearing from Putin, and we continue to back the Ukrainians to the hilt."
Watch: Russia's mobilisation will just mean 'more dead bodies' for Moscow.
It comes after Russia's partial military mobilisation - with 300,000 reservists set to be called up as the Kremlin attempts to regain ground in the face of a counter-attack by Ukraine's forces.
It is Russia's first mobilisation since the Second World War.
In a televised address, Mr Putin also warned the West that Russia would use all the means at its disposal to protect itself, which is being viewed as a reference to Russia's nuclear capability, and said it was "not a bluff".
In response to Putin's comments, Ms Truss said Russia’s president was “desperately trying to justify his catastrophic failures”.
Ms Truss also said the UK will work with its allies to ensure Taiwan can defend itself against China, but refused to go as far as saying the UK would defend it militarily.
Watch: China and Taiwan: How their militaries compare.
The Prime Minister was asked whether she would make the same pledge as US president Joe Biden, who said US forces would defend Taiwan if China invaded.
She told CNN's State Of The Union programme: "What we are very clear about, and I was clear with President Biden, is we support and work with our G7 allies first of all to reduce our strategic dependency on China, and also to make sure that we are standing by our democratic allies around the world.
"And we are determined to work with our allies to make sure that Taiwan is able to defend itself."
"We need to learn the lessons from Ukraine.
"The fact is the free world didn’t do enough to counter Russian aggression early enough and Putin was emboldened to start this appalling war and we can’t see that situation happen in other parts of the world."