Deputy Prime Minister Dominic Raab has said he believes the conflict in Ukraine could last several months or years.
It comes after Vladimir Putin's invasion reaches its 11th day, causing mass death, destruction and evacuations from the country.
Mr Raab appeared on Sky News to warn that the conflict could take "months, if not years" and that the UK must remain resilient in its support for Ukraine.
He told reporter Trevor Phillips: "We ought to be under no doubt that our mission with our allies is to ensure Putin fails in Ukraine and is going to take some time.
"We're talking about months, if not years, and therefore we'll have to show some strategic stamina because this is not going to be over in days."
Mr Raab also warned that Putin will resort to any tactic to achieve victory by looking at his track record in Syria, stating "I don't think that there is any tactic he wouldn't resort to".
"But I would say this. I think NATO and central and eastern European countries are absolutely resolute and we will support them to the hilt".
When questioned why the UK has not imposed sanctions on the Russian defence minister and general of the army, Sergei Soihu, who is leading the invasion, Mr Raab noted that he must be "careful" not to talk about individuals.
He added that to impose sanctions "you need to have evidence he has assets here".
Despite Mr Raab's argument, the EU and US have already sanctioned Mr Shoigu.
In response to this, Mr Raab said: "You've got to have evidence of the legal criteria and he's also got to have assets in the UK".
"If you look at the impact of our sanction, and the UK's been at the vanguard of the international response, I think the fact that Putin and the Russian Central Bank have doubled interest rates to 20 per cent, we think of what the cost of living challenges we're facing."
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