İSTANBUL, Türkiye — Delegations from Russia and Ukraine were to meet in Turkey on Monday for their second round of direct peace talks in just over two weeks, although expectations were low for any significant progress on ending the three-year war after a string of stunning attacks over the weekend.

Ukraine said Sunday it launched a spectacular surprise attack on four Russian airbases thousands of kilometers (miles) apart, destroying more than 40 warplanes. The raid was unprecedented in its scope and geographic reach, targeting bases in Russia’s Arctic, Siberia and Far East more than 7,000 kilometers (4,300 miles) from Ukraine.

The head of the Ukrainian security service, Vasyl Maliuk, who led the planning of the operation, said its success was “a major slap in the face for Russia’s military power.” He said the drones struck simultaneously in three time zones and the complex logistics took over a year and a half to prepare.

Ukrainian President Volodymyr Zelenskyy called it a “brilliant operation.”

Meanwhile, Russia on Sunday fired the biggest number of drones — 472 — at Ukraine since its full-scale invasion in February 2022, Ukraine’s air force said, in an apparent effort to overwhelm air defenses. That was part of a recently escalating campaign of strikes in civilian areas of Ukraine.

Amid the escalation in fighting, the talks in Istanbul appeared unlikely to make much progress.

U.S.-led efforts to push the two sides into accepting a ceasefire have so far failed. Ukraine accepted that step, but the Kremlin effectively rejected it.

The Institute for the Study of War, a Washington-based think tank, said Sunday that “Russia is attempting to delay negotiations and prolong the war in order to make additional battlefield gains.”

The relentless fighting has frustrated U.S. President Donald Trump’s goal of bringing about a quick end to the war. A week ago, he expressed impatience with Russian President Vladimir Putin as Moscow pounded Kyiv and other Ukrainian cities with drones and missiles for a third straight night. Trump said on social media that Putin “has gone absolutely CRAZY!”

Senior officials in both countries have indicated the two sides remain far apart on the key conditions for stopping the war.

The first round of talks, held on May 16, also in Istanbul, ended after less than two hours. While both sides agreed on a large prisoner swap, there was no breakthrough.

Ukraine was triumphant after targeting distant Russian air bases. The official Russian response was muted, with the attack getting little coverage on the state-controlled television. Russia-1 TV channel on Sunday evening spent for a little over a minute on it with a brief Ministry of Defense’ statement read out before images shifted to Russian drone strikes on Ukrainian positions.

Zelenskyy said the setbacks for the Kremlin would help force it to the negotiating table, even as its pursues a summer offensive on the battlefield.

“Russia must feel what its losses mean. That is what will push it toward diplomacy,” he said at a summit Monday in Vilnius, Lithuania with leaders from the Nordic nations and countries on NATO’s eastern flank.

Ukraine has occasionally struck air bases hosting Russia’s nuclear capable strategic bombers since early in the war, prompting the Russian air force to redeploy most of them to the regions farther from the front line.

Because Sunday’s drones were launched from trucks close to the bases targeted in five Russian regions, military defenses had virtually no time to prepare for them.

Many Russian military bloggers chided the military for its failure to build protective shields for the bombers despite previous attacks, but the large size of the planes makes that a challenging task.

The attacks were “a big blow to Russian strategic airpower” and exposed significant vulnerabilities in Moscow’s military capabilities, according to Phillips O’Brien, a professor of strategic studies at the University of St. Andrews in Scotland.

“This is hard to underestimate,” O’Brien wrote in an analysis.

Zelenskyy said that “if the Istanbul meeting brings nothing, that clearly means strong new sanctions are urgently, urgently needed” against Russia.

The Ukrainian delegation led by Defense Minister Rustem Umerov was in place, Heorhii Tykhyi, spokesperson for the Ukrainian Foreign Ministry, said in a message posted on the Ukrainian Embassy WhatsApp group.

The Russian delegation, headed by Vladimir Medinsky, an aide to Russian leader Vladimir Putin, arrived the previous evening, Russian state media reported.

Officials said Turkish Foreign Minister Hakan Fidan would chair the talks, with officials from the Turkish intelligence agency also present.

International concerns about the war’s consequences, as well as trade tensions, drove Asian share prices lower Monday while oil prices surged.

Fierce fighting has continued along the roughly 1,000-kilometer (620-mile) front line, and both sides have hit each other’s territory with deep strikes.

Russian forces shelled Ukraine’s southern Kherson region, killing three people and injuring 19 others, including two children, regional officials said Monday.

Also, a missile strike and shelling around the southern city of Zaporizhzhia, killing five people and injured nine others, officials said.

Russian air defenses downed 162 Ukrainian drones over eight Russian regions overnight, as well as over the annexed Ukrainian peninsula of Crimea, Russia’s Defense Ministry said Monday.

Ukrainian air defenses damaged 52 out of 80 drones launched by Russia overnight, the Ukrainian air force said.

Associated Press writers Suzan Frazer in Ankara, Turkey; Hanna Arhirova in Kyiv, Ukraine, and Geir Moulson in Berlin contributed to this report.

Copyright 2025 Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.