Former cabinet minister David Davis warned that if Nato does not act immediately by offering air support to Ukraine's troops, the country will be defeated "in a matter of days".
And the chair of the Commons Defence Committee, Tobias Ellwood, said Western powers must assist Kyiv with military options including offensive weapons systems and a no-fly zone.
Their comments came shortly before prime minister Boris Johnson hinted in a TV address to the nation that the UK may be ready to make a military contribution to ensuring the Russian assault fails.
“Our mission is clear,” Mr Johnson said. “Diplomatically, politically, economically – and eventually, militarily – this hideous and barbaric venture of Vladimir Putin must end in failure.”
Mr Davis said that, while sanctions should be imposed on Moscow, they will not be enough to deter Putin from pushing ahead with his assault on Russia's neighbour.
And he said that the Russian president would see it as a "legalistic weakness" if Nato confined itself to taking military action under Article 5 only if a member state is invaded.
"Whether we like it or not Putin has effectively declared war on the West," said Mr Davis.
"While we should continue to impose the most ferocious sanctions, they are no longer a deterrent. They are a punishment. They will not stop him.
"If Nato does not act now, Ukraine will be defeated in a matter of days. Therefore if we do not provide military support, more than 40 million Ukrainians will go from living in a democracy to living under a brutal dictatorship.
"It is far too late to get boots on the ground but it is not too late to provide air support to the Ukrainian army which may neutralize Putin's overwhelming armoured superiority.
"If this is confined to the airspace over Ukraine, and is based on a request from (Ukrainian) President (Volodymyr) Zelenskyy, this should be perfectly legal under almost any interpretation of international law. It will also reduce the risk of escalation"
Mr Ellwood said: "We're now moving into a new phase of this .We cannot be timid, we cannot be risk averse. We've got to be more united.
"We've now got to assist Ukraine militarily, and look to see how that can be done. Whether it be with our weapon systems, a no-fly zone, we need to be far more front-footed on this."
The former soldier said that Nato hard power was the only thing that could have deterred Putin from invasion, but that the government had ignored his calls over the past six months for a Nato division to be stationed on Ukrainian soil.
"We tried diplomacy but without any form of carrot and stick that was going to alter Putin's thinking," Mr Ellwood told the BBC. "And we've now tried limited sanctions... hoping perhaps the tanks might turn around.
"I have to say, if Kyiv falls, history will ask why the West didn't do more, why we didn't use our Nato hard power deterrence - the one Western asset that Putin fears. This was not harnessed and we're now seeing the consequences of that."
Former minister Stephen Hammond also called for Nato to deploy its airpower, tweeting: “We must work with our allies to impose tougher sanctions and a no-fly zone.”
Mr Davis said: "Everything now is very risky, but that is the price we are paying for ignoring Putin's provocations on at least five occasions over the last 20 years.
"There are no zero-risk options. If we do not act militarily, then NATO will be significantly weakened and we must fear for the safety of every state that borders Russia."
The calls for military action triggered a scathing response from Boris Johnson’s former top aide Dominic Cummings, who branded Mr Davis “thick as mince” and said it was hypocritical for Conservatives to speak out against Putin now when their party had been “financed by his mates” for years.
“My disgust for westminster is never higher than when it’s excited about war, all the worst of its lies posing cant bullshit idiocy hypocrisy moral cowardice incompetence operational uselessness get turned up to 11,” tweeted the former No 10 adviser.
“Tories literally have their party FINANCED BY PUTIN’S MATES FOR DECADES, won’t even stop them sending their kids to eton/harrow or using London as a ‘laundry’ (London’s *actual Moscow nickname*), then their MPs start babbling about no fly zones!!!”
Join our commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies