Russia is still a “very, very serious” military adversary and should not be underestimated by the West despite its failure to conquer Ukraine as quickly as many had expected, a Royal Marines commander has said.

Brigadier Richard Cantrill, who leads the Marines’ elite 3 Commando Brigade, said that despite the success of Ukrainian forces in repelling Russian troops and destroying their armoured vehicles, Vladimir Putin’s military remains a serious threat.

On Tuesday, Alexander Fomin, the Russian deputy defence minister, said Russia would now enter “phase two” of the conflict and “fundamentally cut back military activity in the direction of Kyiv and Chernihiv”.

Russian forces have been set back by their failure to take control of the airspace above Ukraine, and their armoured vehicles’ vulnerability to anti-tank weapons supplied by Western countries to the Ukrainian military.

The suggestion that Russia has now abandoned the conflict altogether was disputed by Ben Wallace, the Defence Secretary, who said Mr Putin still desired the “systematic occupation and control of Ukraine” and predicted he would now consolidate his strength in the east of the country.

Brig Cantrill, a decorated naval officer who previously worked as assistant head for counter-terrorism and UK operations at the Ministry of Defence, said Russian forces “weren’t in a good place” when the invasion took place and had been met with a “sophisticated” opposition.

He is in Norway working on Exercise Cold Response, a Nato war game in the Arctic designed to prepare Western forces for a Russian invasion in the “High North”.

He said that the Royal Marines’ recent shift to “tactical dispersion” – a technique that involves spreading out a smaller number of troops to achieve an objective behind enemy lines – had been vindicated by the Ukrainians’ success in destroying Russian tanks.

“If I were to take anything, I’m further reassured that our transformation journey that we started last few years is going in the right direction,” he said.

Speaking to The Telegraph from the Bardufoss military base, 200 miles inside the Arctic circle, he said of the Ukrainian defence: “Whatever they’re doing, it seems to be working well. And I think what we’ve seen is that some of the sophisticated anti-tank systems have essentially meant that the urban areas are not viable for the Russians.

“That’s why they are just malletting Mariupol from the flank, which is incredibly sad and disastrous for Ukraine. But it’s also an indication of failure.”

But Brig Cantrill also warned against the idea that Russia should be scaled down as a threat in the mind of Western military powers.

“I think they’re an incredible adversary, not just because of their military capability, but because of their centralised control of all the levers of national power,” he said.

“Putin can sit in the National Defence Centre in Moscow, and can pull on the intelligence service, state media, and military.

“He can do it all in one building, and he doesn’t have to go and get many votes on it.

“So they can become incredibly focused, and their economy is essentially a war economy all the time, so we would never underestimate them.”