The UK will send armoured anti-aircraft vehicles to Ukraine to help Kyiv’s forces as they face a Russian onslaught in the country’s east.

The Stormer vehicle launches Starstreak anti-aircraft missiles which can be used to target planes and helicopters.

Boris Johnson is expected to speak to allies including US President Joe Biden on Monday to discuss Western support for Ukraine as Russian forces focused on capturing the Donbas region.

In his nightly address, Ukrainian President Volodymyr Zelensky said: “It can now be stated that Russian troops have begun the battle for Donbas, for which they have been preparing for a long time.

“A very large part of the entire Russian army is now focused on this offensive.”

The supply of the Stormer to Ukraine comes after the UK invited Ukrainian generals to Salisbury Plain earlier this month to see the military kit which could be available to them, including armoured vehicles.

The provision of Stormers – reported by The Sun – has not yet been officially confirmed, but Defence Secretary Ben Wallace is expected to update MPs this week.

A defence source said: “It is no secret that the UK has committed to helping Ukraine with its anti-air capabilities.

“The Defence Secretary will be making a statement to Parliament this week.”

In the latest sign of the West stepping up support for Mr Zelensky, the White House said Mr Biden will convene a secure video call with allies on Tuesday to discuss support for Ukraine and efforts to hold Vladimir Putin’s Russia accountable.

In the UK, Cabinet minister Brandon Lewis said “we will be sending out further defensive arms” to Ukraine.

“We’re seeing a further push, it seems, from Putin’s regime, so we will continue to do all we can to support Ukraine,” the Northern Ireland Secretary told BBC Breakfast.

“As the Prime Minister said when he was in Kyiv with the president (Volodymyr Zelensky) just a week or so ago, we will be sending out further defensive arms.”

Mr Lewis said he could not comment on suggestions of a prisoner exchange when asked about reports of Britons captured while fighting for the Ukrainian military.

He added: “People should not be taking what is in reality an illegal route through into a very dangerous situation.

“I hope you can appreciate I’m not going to comment on the situation on the two individual cases that you reference.

“But we really should be very clear with people, that isn’t what they should be doing. There are ways to support Ukraine and that is the official ways on the Government website that people can follow.”

In footage reportedly broadcast on Russia’s Rossiya 24 on Monday, Shaun Pinner addresses the Prime Minister and appears to ask for himself and fellow British prisoner of war Aiden Aslin to be swapped for pro-Kremlin politician Viktor Medvedchuk, who has been held in Ukraine.

Shadow attorney general Emily Thornberry said “we should be negotiating with the Russians to try to get them back”, but “I don’t think that we can give in to blackmail”.

“We need to make it clear that we don’t negotiate and give in to blackmail when it comes to hostages, and we’ve always said that we need to stick to that,” she told Sky News.