Ukrainian soldiers have travelled to Britain to learn how to use UK-supplied armoured vehicles to aid in their war against Russia, Prime Minister Boris Johnson said.

"A couple of dozen" troops arrived last week to train on the 120 Mastiff, Wolfhound and Husky armoured vehicles being supplied to Kyiv, an official confirmed.

"I can say that we're currently training Ukrainians in Poland in the use of the anti-aircraft defences and actually in this country (the UK) in the use of the armoured vehicles," he told UK media during a visit to India.

The vehicles are designed to be used in offensive operations alongside tanks and infantry vehicles.

Johnson's spokesman said more were expected to travel in the future.

"We are moving in conjunction with our allies providing new types of equipment that perhaps the Ukrainians wouldn't have had previous experience on," the spokesman said. 

"So it's only sensible that they get the requisite training to get the best use of it."

The UK has taken a leading role in arming and training Ukraine's forces, especially for anti-tank missiles.

Johnson earlier this month became the first G7 leader to visit Kyiv since Russian President Vladimir Putin launched his offensive on February 24. 

The spokesman denied that training the Ukrainians in Britain would risk escalating the conflict.

"We're always conscious of anything that's perceived to be escalatory but clearly what's escalatory is the actions of Putin and his regime," he said.