In July, as he secretly readied an invasion of Russia, President Volodymyr Zelensky of Ukraine sent a very different signal in public: He wanted talks to end the war.

Speaking to the BBC, Mr. Zelensky said he had a plan to end the “hot stage” of the war this year. He dispatched his foreign minister on a surprise trip to China, a mission to improve Ukraine’s relationship with Russia’s most important partner. And he pushed for a series of international meetings, including one planned for Qatar in August, in which he hoped to rally backing for Ukraine’s positions and pave the way for a broader settlement.

His summer overtures departed from the two years of Mr. Zelensky’s refusing to offer any hint of concessions in the face of a Russian invasion that many Ukrainians believe aims to wipe their country off the map. And they made it all the more stunning when on Aug. 6, Ukrainian forces rolled into Russia’s Kursk region, delivering one of the most embarrassing moments for President Vladimir V. Putin in 30 months of war and confounding predictions that the two countries might be headed toward a cease-fire.

Kyiv is making a risky bet: that the incursion gives it new leverage for a favorable deal with the Kremlin, even as its military remains on the defense across much of the front line in Ukraine. Russians who know Mr. Putin expect him to lash out in response, believing that his military has the upper hand in personnel and weaponry.

There are already signs that cease-fire efforts suffered a setback. A diplomat involved in the talks said that Russian officials postponed a meeting planned to be held in Qatar this month to negotiate a deal in which both sides would stop attacks on each other’s energy infrastructure. The postponement was reported earlier by The Washington Post.

In comments reported on Monday by Russian state media, Mr. Putin’s foreign policy adviser, Yuri Ushakov, said, “At the current stage, given this escapade, we are not going to talk.” The length of any pause in negotiations, Mr. Ushakov added, “depends on the situation, including on the battlefield.”

Grigory A. Yavlinsky, a longtime Russian politician who met with Mr. Putin last October to promote the idea of a cease-fire, said in an interview from Moscow that there had been hope in the Russian capital that “the fighting would stop this year.”

“The circumstances that have just happened,” he added, “they have lowered all these chances, they have removed them from the agenda.”

To many Ukrainians, Mr. Putin’s focus has never been peace, but rather the complete domination of their country. Officials in Kyiv say the incursion into Kursk could help provide the leverage they need to achieve a deal on Ukraine’s terms. They say that only by making more Russians — and Mr. Putin himself — feel the pain of war can they force the Kremlin to back down.

“It’s very hard to imagine peace in our era unless Russia loses,” Yaroslav Yurchyshyn, a member of Ukraine’s Parliament, said in an interview. “The only solution to anything with Russia is: Make them pay.”

Ukraine’s counterattack into Russia will hasten talks, he said, by raising the cost of war on Russia. Ukrainian officials insist that Mr. Zelensky’s public diplomatic outreach this summer, coupled with his secret planning for the Kursk offensive, were two prongs of the same strategy.

“They’ve thought through how military and diplomatic maneuvers could work together,” Evelyn Farkas, the director of the McCain Institute, said of Ukraine’s approach. “It’s not just smart in the context of setting them up for peace talks today, it’s putting pressure on Russia and reminding the Russians they don’t control the narrative.”

It is far from clear that the combination of military and diplomatic pressure will work with Mr. Putin, who has so far faced down political and economic headwinds at home and shown he is willing to bear a heavy cost to defeat Ukraine.

Ukraine’s position has been shifting in recent months.

In June, Mr. Zelensky spearheaded a 92-country gathering in Switzerland meant to win global support for his vision of a “just and lasting peace.” The plan as outlined would eventually mean Ukrainian membership in NATO, a full Russian withdrawal and prosecutions of Russians for war crimes.

But China skipped the summit, and some of the leading non-Western countries in attendance, including India, Indonesia, Saudi Arabia and South Africa, refused to sign on to the summit’s joint declaration. To those countries, a key problem was that Russia was not invited to the Swiss summit; any peace talks, they said, needed to involve both sides and a willingness to compromise.

In the ensuing weeks, Mr. Zelensky showed an increasing openness to negotiate with Russia directly. He said that Russia could be invited to a second “peace summit” this year, and that Ukraine could regain its territory through negotiations.

Outreach to neutral countries has continued. Prime Minister Narendra Modi of India plans a visit to Ukraine, the Indian Foreign Ministry said on Monday.

Ukraine has also sought to set up a series of interim meetings focusing on specific issues. The first such meeting was set to be held in Qatar this summer, Mr. Zelensky said in July, on energy security; further meetings would come, in Turkey and in Canada, on food security, prisoners of war and Ukrainian children who had been taken to Russia.

Even as Ukraine was signaling its readiness to talk, its military was preparing for one of its most daring attacks since Mr. Putin’s invasion began in February 2022.

But Ukrainian officials have also insisted that diplomacy and taking the war onto Russian territory are not contradictory efforts. And Ukrainian analysts have pointed out that Ukrainian strikes on oil refineries that began last winter provided leverage to negotiate on Russian attacks on Ukraine’s electrical power plants, a military tactic that led to the planned talks in Qatar.

“To engage Russia in a fair negotiation process, the Russians need to face tactical defeats on the battlefield,” Mykhailo Podolyak, a senior presidential adviser, said in an interview on Aug. 6, the day the Kursk incursion started. “As these defeats pile up, social unrest will start to stir within Russia.”

There are signs that Ukraine’s attack has already unsettled many Russians. A Russian state-controlled pollster, F.O.M., published weekly survey results on Friday in which 45 percent of respondents said those around them were in an “anxious mood,” a 12-point jump from two weeks earlier. It was a spike in anxiety similar in magnitude to the one after the terrorist attack at a concert hall near Moscow in March.

But Russians who know Mr. Putin said they doubted that the Kursk incursion and any ensuing public unrest could force the Russian leader to change course. The fundamentals of the fighting, they noted, have remained unchanged, with Mr. Putin convinced that he has the resources to outlast Ukraine and the West. Russia continues to dominate along much of the front in Ukraine and to make gains in the east, closing in on the strategically important Ukrainian city of Pokrovsk.

Projecting business as usual, Mr. Putin flew to Azerbaijan on Sunday for a two-day visit. The Kremlin released footage of him relaxing on a couch in shirtsleeves, top shirt buttons undone, with Azerbaijan’s authoritarian president, Ilham Aliyev, and Mr. Aliyev’s wife, Mehriban Aliyeva.

Mr. Putin has said nothing about the incursion since a tense, televised crisis meeting on Aug. 12, when he questioned whether there was any use for negotiations with Ukraine, without ruling them out entirely.

“The enemy is apparently trying to improve its future negotiating positions,” Mr. Putin said. He claimed, without evidence, that Ukraine was firing at civilians, and added: “What is there to even talk about with them?”

Russia postponed its participation in the Qatar meeting on energy security after the Kursk incursion, the diplomat briefed on the matter said, speaking on the condition of anonymity to discuss sensitive matters. Russia did not pull out of the talks but said it needed more time, describing the incursion as an escalation, the diplomat said.

Last Tuesday — a week after the incursion began — Andriy Yermak, the head of Mr. Zelensky’s presidential office, said the meeting on energy security was still set to take place this month but in an online format. A spokesman for Mr. Zelensky’s office declined to comment.

Since the Kursk incursion, Mr. Putin will now be looking for ways to increase the amount of pain he is inflicting on Ukraine, said Tatiana Stanovaya, a senior fellow at the Carnegie Russia Eurasia Center. Rather than negotiate, Mr. Putin is convinced that Russia will eventually triumph, she said, and he is prepared to take on more risk and force Russians to carry a heavier cost.

“Putin is ready to pay an even higher price than this,” she said, referring to the consequences of the Kursk incursion. “For Putin, this is simply a question of the price of victory.”

Constant Méheut, Evelina Riabenko and Stanislav Kozliuk contributed reporting from Kyiv.