KYIV, Ukraine (AP) — Russia pounded four Ukrainian cities overnight into Wednesday, injuring at least 15 people in an attack that mostly targeted energy infrastructure, officials said.

The latest bombardment in Russia's escalating aerial campaign against civilian areas came ahead of a Sept. 2 deadline set by U.S. President Donald Trump for the Kremlin to reach a peace deal in the three-year war, under the threat of possible severe Washington sanctions if it doesn't.

No date has yet been publicly set for a possible third round of direct peace talks between delegations from Russia and Ukraine. Two previous rounds delivered no progress apart from prisoner swaps.

Russia launched 400 Shahed and decoy drones, as well as one ballistic missile, during the night, the Ukrainian air force said. The strikes targeted northeastern Kharkiv, which is Ukraine's second-largest city, President Volodymyr Zelenskyy's hometown of Kryvyi Rih in central Ukraine, Vinnytsia in the west and Odesa in the south.

Russia does not change its strategy," Zelenskyy said. "To effectively counter this terror, we need a systemic strengthening of defense: more air defense, more interceptors, and more resolve so that Russia feels our response.

Trump on Monday pledged to deliver more weapons to Ukraine, including vital Patriot air defense systems, and threatened to slap additional sanctions on Russia. It was Trump's toughest stance toward Russian President Vladimir Putin since he returned to the White House nearly six months ago.

But some U.S. lawmakers and European government officials expressed misgivings that the 50-day deadline handed Putin the opportunity to capture more Ukrainian territory before any settlement to end the fighting.

Other U.S. ultimatums to Putin in recent months have failed to persuade the Russian leader to stop his invasion of neighboring Ukraine. Tens of thousands of soldiers have been killed in the war, many of them along the more than 1,000-kilometer (620-mile) front line, and Russian barrages of cities have killed more than 12,000 Ukrainian civilians, the United Nations says.

The Institute for the Study of War, a Washington think tank, said Tuesday that "Putin holds a theory of victory that posits that Russia can achieve its war aims by continuing to make creeping gains on the battlefield indefinitely and outlasting Western support for Ukraine and Ukraine's ability to defend itself."

Trump said the U.S. is providing additional weapons for Ukraine but European countries are paying for them. While Ukraine and European officials were relieved at the U.S. commitment after months of hesitation, some hoped Washington might shoulder some of the cost.

"We welcome President Trump's announcement to send more weapons to Ukraine, although we would like to see the U.S share the burden," European Union foreign policy chief Kaja Kallas said Tuesday. "If we pay for these weapons, it's our support."