Residents of Ukraine’s capital stepped out into smoke-filled streets on Saturday morning after a barrage of Russian ballistic missiles killed at least nine people — only to learn that President Trump had backed away overnight from a promise to let Ukraine produce Patriot air-defense systems designed to stop such missiles.

Mr. Trump’s reversal was likely to come as a bitter disappointment in Ukraine, where officials have warned for months that dwindling stocks of Western-supplied Patriot interceptors are leaving the country increasingly vulnerable to Russia’s intensifying missile campaign.

Ukraine’s president, Volodymyr Zelensky, said that only one of the 27 ballistic missiles that Russia fired overnight at the capital, Kyiv, and other cities had been shot down “because there are no interceptors for the Patriot systems.”

“And it is this shortage of ballistic missile interceptors that only encourages Russia to launch such attacks that take human lives,” Mr. Zelensky wrote on social media. His post included a video of the attack’s aftermath, which showed firefighters dousing burning buildings and rescuers carrying away a body in a black bag.

Mr. Trump’s backtracking on his decision to let Ukraine manufacture U.S.-designed Patriots under license will make little difference for Kyiv in the short term. Experts had cautioned that it would take quite some time for Ukraine to start actually manufacturing the complex Patriot interceptors.

Still, Mr. Trump’s authorization had been welcomed as an opportunity to strengthen Ukraine’s air defenses over the long term, as the fighting increasingly shifts to long-range strikes targeting military sites, energy infrastructure and logistics hubs. More recently, the fighting has also spread across the Black Sea, with both sides targeting commercial vessels. On Saturday, Ukraine hit and sank a ship operated by Rosatom, the Russian nuclear giant.