Britain is releasing another $100 million to help Ukraine, Prime Minister Boris Johnson announced Sunday and promised fresh efforts to rally international opinion against Russia's invasion.

The $100 million, to be provided via the World Bank, is in addition to the £220 million ($290 mln) of overall aid support to Ukraine, said a statement from Downing Street.

The new funding will go towards keeping key state functions operating, it added.

"While only (Russian President Vladimir) Putin can fully end the suffering in Ukraine, today's new funding will continue to help those facing the deteriorating humanitarian situation," said Johnson.

The British leader will on Monday receive the Dutch and Canadian prime ministers, Justin Trudeau and Mark Rutte and they will visit a Royal Air Force base before holding a joint news conference.

On Tuesday, Johnson will meet the leaders of the four Visegrad countries, Hungary, Poland, the Czech Republic and Slovakia.

This week's meetings are part of a six-point plan that Johnson's office unveiled on Saturday designed to ensure Russia's invasion of Ukraine fails.