Ukraine President Volodymyr Zelenskyy asked other nations to ban Russian energy exports, which he said are enabling Moscow's invasion of his country.
"Oil is one of the two sources of Russian self-confidence, their sense of impunity," he said in the late night address. "Another source — gas — will also be shut down over time. It's just inevitable."
Zelenskyy late Friday emphasized the need for a war crimes tribunal for Russia and for more weapons support to Ukraine.
British Prime Minister Boris Johnson met with Zelenskyy in Kyiv, where he pledged more military and financial support to the embattled country. London is sending armored vehicles and anti-ship missile systems ahead of an expected Russian offensive in eastern Ukraine.
Russian forces are concentrating their efforts in the country's east as thousands of people try to flee the region. Russian air attacks over Ukraine's south and east are expected to increase in the coming days, though it continues to face stiff Ukrainian resistance.
Several world leaders have fiercely condemned a missile attack on an eastern Ukrainian train station in Kramatorsk that killed at least 52 people, with the EU introducing new sanctions on Russian individuals.