Ukraine’s President Volodymyr Zelenskiy warned on Sunday against further Russian attacks on energy infrastructure, while the mayor of Kyiv urged residents to consider temporarily leaving if the capital’s water and power supplies were disrupted.

In his nightly remarks, Zelenskiy stated that Russia was “concentrating forces and resources in preparation for a possible repeat of mass attacks on our infrastructure First and foremost, there is energy.”

More than 4.5 million consumers were already without power, he added, amid concerns that support for Ukraine could waver as the war’s impact on energy and food prices persists into winter.

U.S. national security adviser Jake Sullivan, who travelled to Kyiv on Friday and pledged Washington’s “unwavering and unflinching” support for Ukraine, has held undisclosed talks with Russian officials designed to avoid further escalation, the Wall Street Journal said on Sunday.

News of those contacts followed a report that Washington was urging Kyiv to signal an openness to talks with Russia.

Presidential adviser Mykhailo Podolyak said earlier on Twitter that Ukraine would “stand” despite Russian attacks on its energy infrastructure, by marshalling air defence, protecting infrastructure and optimising consumption to do so.

The country faced a projected shortfall of 32 percent in power supply on Monday, Sergei Kovalenko, the chief executive of YASNO, a major provider of energy to the capital, said on his Facebook page.

The warnings followed remarks by Kyiv Mayor Vitali Klitschko urging residents to “consider everything”, including a worst-case scenario in which the capital loses power and water.

Residents should consider “spending some time” with friends or family outside the city, he said in a television interview on Saturday, in which he accused Russian President Vladimir Putin of deliberately targeting civilian infrastructure.

“His task is for us to die, to freeze, or to make us flee our land so that he can have it. That’s what the aggressor wants to achieve,” Klitschko added.

In the south, Russia and Ukraine continued to trade accusations as Ukraine advances on the city of Kherson. Reuters was unable to immediately verify battlefield accounts from either side.

Regional governor Yaroslav Yanushevych said Russian forces destroyed about 1.5km of power lines, cutting supply to the city of Beryslav.

“It is likely that there will be no electricity in Beryslav until it is fully freed from occupation,” Yanushevych wrote on the Telegram messaging app, adding that power lines to Kherson had also been destroyed.

On Sunday, Russian news agencies said shelling by Ukrainian forces damaged Ukraine’s vast Russian-held Nova Kakhovka dam, upstream of Kherson on the Dnipro river. They gave no supporting evidence, and Reuters could not immediately verify the reports.

Russian state-owned TASS quoted an emergency services representative as saying a rocket launched by a U.S.-made HIMARS missile system had hit the dam’s lock, damaging it.

The official called the incident an “attempt to create the conditions for a humanitarian catastrophe” by breaching the dam.

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The warnings came as the Wall Street Journal said Sullivan held confidential conversations in recent months with Kremlin aide Yuri Ushakov and Russian Security Council secretary Nikolai Patrushev that were not disclosed publicly.

Few high-level contacts between U.S. and Russian officials have been made public in recent months, as Washington has insisted that any talks on ending the war in Ukraine be held between Moscow and Kyiv.

The White House declined to comment on the report, responding only with a statement attributed to National Security Council spokesperson Adrienne Watson: “People claim a lot of things.”

On Saturday, the Washington Post said the United States is privately encouraging Ukraine to signal an openness to negotiate with Russia, as the State Department said Moscow was escalating the war and did not seriously wish to engage in peace talks.

The paper cited unidentified sources as saying the request by American officials was not aimed at pushing Ukraine to the negotiating table, but a calculated attempt to ensure Kyiv maintains the support of other nations.

Zelenskiy signed a decree on Oct. 4 formally declaring the prospect of any Ukrainian talks with Putin “impossible” but leaving the door open to talks with Russia.

The White House National Security Council had no immediate comment on the accuracy of the report.

A State Department spokesperson responded: “We’ve said it before and will say it again: Actions speak louder than words. If Russia is ready for negotiation, it should stop its bombs and missiles and withdraw its forces from Ukraine.”