British Prime Minister Boris Johnson told Ukrainian President Volodymyr Zelenskyy on Sunday that Britain would continue to pursue more options for bolstering Ukraine's "self-defense" amid conflict with Russia. 

In a separate phone call, Ukrainian Foreign Minister Dmytro Kuleba and UK Foreign Secretary Liz Truss discussed next steps for imposing more sanctions on Russia.

"Pressure must increase until Russia ceases its meaningless aggression and stops barbaric war crimes. Grateful to the UK for stepping up support for Ukraine," Kuleba wrote on Twitter early Monday.