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

The United States is by far Kyiv’s biggest supplier of wartime support, and Ukraine is trying to fend off an intense Russian offensive in eastern areas of the country. The push is focused on the Ukrainian border regions of Kharkiv and Donetsk but Ukrainian officials say it could spread wider as Russia's bigger army seeks to make its advantage tell.

The offensive is seeking to exploit Kyiv’s shortages of ammunition and troops along the roughly 1,000-kilometer (620-mile) front line.

That shortfall in weaponry came after U.S. military aid was held up in Congress for six months before Biden in April signed into law a $61 billion military aid package for Ukraine.

Amid Russia's most recent onslaught and with Ukraine's army reeling, some NATO allies including the U.S. said last week they would allow Ukraine to use weapons they deliver to Kyiv to carry out limited attacks inside Russia.

That step brought a furious response from the Kremlin, which warned that Europe's biggest conflict since World War II could spin out of control.

Biden and Zelenskyy attended the 80th anniversary events of D-Day in Normandy, northern France, on Thursday, along with European leaders who have supported Kyiv’s efforts in the war.

Biden pledged “we 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.

Ukraine depicts its fight against the Kremlin's forces as a clash between Western democratic freedom and Russian tyranny. Russia says it is defending itself against a menacing eastward expansion of the NATO military alliance.

The U.S. will send about $225 million in military aid to Ukraine, U.S. officials said Thursday. The new package includes munitions for the High Mobility Artillery Rocket System, or HIMARS, as well as mortar systems and an array of artillery rounds., officials said

French President Emmanuel Macron announced that France will provide Ukraine with its Mirage combat aircraft.

Macron has been a vocal supporter of Ukraine. He said in February that putting Western troops on the ground in Ukraine is not “ruled out.”

Zelenskyy began a day of meetings in Paris on Friday with an official welcome ceremony at the golden-domed Invalides monument, site of Napoleon’s tomb.

During the day, Zelenskyy was due to visit the Nexter arms manufacturer in Versailles, which makes the Caesar self-propelled howitzers that France, among other weapons, is providing to Kyiv’s forces.

He was also to make a speech to the National Assembly, which is the lower house of France’s parliament, and meet with French President Emmanuel Macron at the Élysée Palace.

Zelenskyy’s foreign trips aim to keep Ukraine’s plight in the public eye, secure more military help for its fight against Russia’s invasion and lock in long-term Western support through bilateral alliances.

France and Ukraine in February signed a 10-year bilateral security agreement. Zelenskyy has since signed similar bilateral agreements with many European countries.

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Follow AP’s coverage of the war in Ukraine at https://apnews.com/hub/russia-ukraine