PARIS (AP) — U.S. President Joe Biden will meet with Ukrainian President Volodymyr Zelenskyy in Paris as Kyiv’s army endures its hardest days of fighting since the early weeks of the Russian invasion and prepares for what officials say could be a tough summer ahead.

The United States is Kyiv’s biggest supplier of wartime support as Ukraine tries to fend off an intense Russian offensive in eastern areas of the country.

Biden and Zelenskyy attended the 80th anniversary events of D-Day in Normandy, in northern France, on Thursday.

Biden pledged the United States “will not walk away” from Ukraine, drawing a direct line from the fight to liberate Europe from Nazi domination to today’s war against Russian aggression.