KYIV, Ukraine — Russia launched more than 100 Shahed and decoy drones at Ukraine in nighttime attacks, the Ukrainian air force said Monday, after the Kremlin effectively rejected an unconditional 30-day ceasefire in the more than three-year war, but reiterated it would take part in possible peace talks later this week without preconditions.

There was no direct response from the Kremlin, meanwhile, to Ukrainian President Volodymyr Zelenskyy’s challenge for Russian leader Vladimir Putin to meet him for face-to-face peace talks in Turkey on Thursday.

Kremlin spokesman Dmitry Peskov on Monday refused to say who might travel to Istanbul from the Russian side.

“Overall, we’re determined to seriously look for ways to achieve a long-term peaceful settlement. That is all,” Peskov said.

The United States and European governments are making a concerted push to stop the fighting, which has killed tens of thousands of soldiers on both sides, as well as more than 10,000 Ukrainian civilians. Russia’s invading forces have taken about one-fifth of Ukraine in Europe’s biggest conflict since World War II.

U.S. President Donald Trump said Monday that he’s optimistic about the Istanbul talks. There is “the potential for a good meeting” between Putin and Zelenskyy, Trump said in Washington, adding that he was “thinking about flying over” to the talks from his visit to Qatar and the United Arab Emirates that day.

Zelenskyy supported the prospect of Trump attending the negotiations.