The idea of "freezing" the war in Ukraine was put forward recently by a senior member of Germany's governing Social Democrats.

"In 2014 they froze the conflict, and Ukraine had 18,000 soldiers murdered on the front line between 2014 and the invasion," Wallace said in an interview with dpa on Thursday.

"Russia would re-arm, re-equip and do what it did after 2014. And it would come back later," he added.

"So the problem with the freeze is, you'd have to guarantee it," Wallace said. But he noted that Ukraine would not be persuaded either, as Britain, the US, Germany and France had all tried to give their guarantees to keep helping Kyiv in the past.

"So, if you're Ukrainian, would you really trust our guarantee at the moment? And what would you give Ukraine to persuade them to freeze?" he questioned, adding: "They might say, Give us membership of NATO. Right, draw a new line, wherever the line is, but what's left: NATO."

Asked to speculate as to whether Ukraine might be willing to accept NATO membership in exchange for stopping fighting for territory occupied by Russia, Wallace refused to be drawn.

"France and Germany will never go for that," he said. "I don't like to get to the speculation of what the deal should be. It's for Ukraine to decide, they are the ones who've lost thousands of people. And they're the ones fighting for us right now. We're not fighting."

"I don't think Russia would go for it either," Wallace added. "I mean, Russia would say no, but ultimately, we'd have to get Russia in a position where it knows it's got something to lose."