Russia launched its most devastating attack on Kyiv this year, killing at least 12 people and injuring dozens more in a missile and drone barrage that triggered a rare and direct rebuke from U.S. President Donald Trump, who urged Russian President Vladimir Putin to halt the violence.

“Vladimir, STOP!” Trump said in a sharply worded statement from the White House on Thursday, condemning the strike as “not necessary” and “very bad timing” amid ongoing peace negotiations aimed at ending the war in Ukraine.

The assault on the Ukrainian capital, which destroyed buildings, ignited fires, and left at least 90 people injured, came as both Kyiv and Moscow seek to demonstrate progress in response to Trump’s calls for a swift resolution to the two-year conflict.

Despite the escalation, Trump expressed optimism that a peace deal was within reach, telling reporters: “These next few days are going to be very important. Meetings are taking place right now. I think we’re going to make a deal … I think we’re getting very close.”

He added that the Kremlin had made a “pretty big concession” by signaling openness to ending the war and halting its efforts to capture all of Ukraine.

Russian Foreign Minister Sergey Lavrov, in an interview with CBS News, echoed cautious optimism, saying negotiations were “moving in the right direction,” though he noted some details still needed to be resolved.

Trump revealed that pressure was also being applied to Kyiv to come to terms. Secretary of State Marco Rubio confirmed that more discussions were planned for the weekend and emphasized the U.S. desire to see both Ukraine and Russia take decisive steps toward finalizing a peace agreement.

Following consultations in Washington, NATO Secretary-General Mark Rutte said Ukraine was engaging seriously in negotiations. “There is something on the table now where the Ukrainians are really playing ball,” he said. “The ball is clearly in Russia’s court now.”

Trump later reiterated his position on social media platform Truth Social: “I am not happy with the Russian strikes on KYIV. Not necessary, and very bad timing. Vladimir, STOP! 5000 soldiers a week are dying. Let’s get the Peace Deal DONE!”

Asked whether he believed Putin would respond to his appeal, Trump replied, “I do.”

However, the White House warned that U.S. support for the diplomatic effort might wane if progress stalls. Trump also criticized Ukrainian President Volodymyr Zelensky on Wednesday for refusing to recognize Russia’s annexation of Crimea, saying on Thursday that reclaiming the territory would be “very difficult.”

While Trump’s tone toward Putin remained relatively conciliatory, referring to Russia’s moves as missteps rather than provocations, he has taken a far harsher stance toward Zelensky, even calling him a “dictator” in previous remarks.

According to U.S. officials, Trump’s special envoy is scheduled to meet with Putin on Friday to advance negotiations.