Johnson is expected to meet Crown Prince Mohammed bin Salman this week, hoping he can persuade him to boost the Gulf state's oil production to offset the impact of economic sanctions against the Kremlin on global energy prices.

The Organization of the Petroleum Exporting Countries (OPEC) said on Tuesday that oil demand in 2022 faced challenges from Russia's invasion of Ukraine and rising inflation as crude prices soar.

Europe must protect its own security by helping Ukraine defend itself against Russia, Ukrainian President Volodymyr Zelenskiy told a meeting of Joint Expeditionary Force leaders in London via video link on Tuesday, urging them to send more weapons.

British Prime Minister Boris Johnson is hosting a summit of Nordic and Baltic leaders to discuss European defence and security.

"We all are the targets of Russia and everything will go against Europe if Ukraine won't stand so I would like to ask you to help yourself by helping us," Zelenskiy told the leaders.

Over 100,000 Britons have expressed interest in hosting Ukrainian refugees, as part of a government programme for households to take in those fleeing Russia's invasion.

The scheme enables individuals, charities, community groups and businesses to volunteer accommodation for refugees for a minimum of six months.

It is open to Ukrainian nationals and their immediate family members and will allow them to live and work in the UK for up to three years and access healthcare, benefits and education.

Hosts, who will be given £350 ($457, 418 euros) a month, must submit the names of those they wish to sponsor, with NGOs and charities working to identify those most in need.

The UK has faced criticism over its policy towards those fleeing the violence in Ukraine, with places limited to those who already have family in the country.

But Johnson has defended the scheme, insisting last week the country was "absolutely determined to be as generous as we possibly can be".

(With inputs from agencies)