KYIV/WASHINGTON: The Ukrainian president warned on Sunday that more Russian attacks on his country's energy infrastructure were possible, as the government advised residents in Kyiv to plan to leave as ongoing strikes threaten power supplies.

A nightly address by Zelensky said Russia was concentrating forces and means in preparation for mass attacks on infrastructure. Firstly, energy.

More than 4.5 million consumers were already without power, Zelenskiy said, amid concerns support for Ukraine's cause could waver as the war's impacts on energy and food prices persist into winter.

Presidential adviser Mykhailo Podolyak said earlier on Twitter that Ukraine would "stand" despite Russian attacks on its energy infrastructure, adding that this would be done by using air defence, protecting infrastructure and optimising consumption.

The country faced a 32 per cent deficit in projected power supply Monday, Sergei Kovalenko, CEO of YASNO, a major supplier of energy to the capital, said.

The warnings followed remarks by Kyiv Mayor Vitali Klitschko urging residents to "consider everything" including a worst-case scenario where the capital loses power and water.

Yaroslav Yanushevych, governor of the Kherson region, said Russian forces destroyed about 1.5km of power lines, cutting the power 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 leading to Kherson had also been destroyed.

Russian news agencies reported on Sunday that Ukraine's vast Russian-held Nova Kakhovka dam, upstream of Kherson on the Dnipro river, was damaged in shelling by Ukrainian forces. The reports provided no evidence to support the allegation, which could not be immediately verified by Reuters.

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.

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.

Zelensky 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.