Defence Secretary Ben Wallace urged all the Conservative Party leadership candidates to "recognise the importance" of defence spending amid cross-party calls to rethink army cuts.
Mr Wallace spoke of the importance of continued support for Ukraine despite the change of leadership in Number 10, telling MPs "it is important that we don't give up on this" and "we must stick at it as long as it takes".
His comments during Commons defence questions came as Conservative MP Mark Francois said the "supposed 10,000 cuts" in the Army "should not only be reviewed but completely reversed".
The Defence Secretary replied by stating he "would recommend to all the leadership candidates who (are) wanting their votes from this side, that they recognise the importance" of defence spending.
"I think what I can say is the threat has changed and that threat does warrant more spending on defence, because the world is more dangerous and more anxious than it was, not only when we had the defence command paper, but when it was before Putin invaded," he continued.
Watch: Who is winning the war in Ukraine?
Mr Wallace said the Ministry of Defence (MOD) will "review the threat as it changes" when asked to rethink plans to cut the British Army by a further 10,000 troops.
Shadow defence secretary John Healey said Mr Wallace had been in his role since Boris Johnson pledged he wouldn't cut the Armed Forces during the last election.
"So will he now do what we've been urging from these benches for over a year and rethink these cuts to the strength of the British Army?" Mr Healey asked.
The Defence Secretary replied "he will be aware that the Defence Command Paper was written and delivered before the actual Russian invasion of Ukraine and I have said continually we will review that when it comes in".
Watch: UK's support for Ukraine not affected by Boris Johnson's departure, Defence Secretary says.
"And we will obviously review the threat as it changes," he said.
"It is an ongoing review of the threat, that’s why we have defence intelligence giving regular briefings and, of course, next year or the year after is our spending moment for this department."
He also warned "Putin's one calculation is that we will all get bored and go back to doing other things, that's how Russia wins, we're not going to let them win".
Mr Wallace added "as long as [he is] Defence Secretary" the support to Ukraine will continue.
"I obviously can't speak for the next prime minister, but what I can say is all of the candidates have clearly made a statement as such," he said.
"It is important that we don’t give up on this, we carry on whoever comes next and the next Government after the next election.