Washington — President Volodymyr Zelenskyy of Ukraine urged President Trump and Congress to expand deliveries of Patriot missile systems in a letter written on Memorial Day, warning that Russia is preparing a broader campaign of ballistic missile attacks against Ukrainian cities.

CBS News obtained the five-page letter, which framed Ukraine's fight against Russia not simply as a regional war, but as a test of American leadership and the durability of Western alliances.

"And when it comes to defending against ballistic missiles, we rely almost exclusively on the United States," wrote Zelenskyy. "Patriot systems remain the most effective defense against every type of Russian ballistic missile." 

He added: "And it is in Ukrainian hands that Patriot systems have proven something extremely important: the majority of Russian missiles can be stopped."

The appeal comes as Ukraine faces mounting pressure from intensified Russian aerial bombardments and growing uncertainty over the pace of Western military assistance. Zelenskyy described a massive Russian assault carried out on the eve of Memorial Day, saying Moscow launched dozens of cruise and ballistic missiles, including hypersonic weapons, alongside roughly 600 drones. 

The strikes killed at least two people, and nearly 100 people were injured. More than 350 residential buildings were damaged, among them schools and museums in Kyiv, including the Chornobyl Museum, which had recently been renovated ahead of the 40th anniversary of the Chornobyl disaster. The museum was destroyed by a direct missile strike, according to Zelenskyy's letter. 

The letter appeared calibrated not only to secure military aid, but also to reinforce Ukraine's strategic value to the U.S. at a moment when Washington is balancing commitments in Europe, the Middle East and Asia. 

Zelenskyy underscored that Patriot interceptors are incredibly difficult to obtain quickly enough to counter Russia's expanding ballistic missile campaign. The embattled president said while he's "grateful" for the Prioritised Ukraine Requirements List, the NATO-backed procurement mechanism created to keep U.S.-made weapons flowing to Ukraine, the "current pace of deliveries through the PURL program is no longer keeping up with the reality of the threat we face."

The Kviv Independent first reported on the letter Wednesday.