Kyiv (Ukraine) (AFP) - Kyiv on Sunday denounced as dangerous lies suggestions from Russia that Ukraine was preparing to use a "dirty bomb" as a dramatic escalation in their eight-month-old war.

Ukraine's western allies also dismissed the allegations from Moscow, just hours after Russia went public with the startling claims.

In conversations with his British, French and Turkish counterparts, Russian Defence Minister Sergei Shoigu conveyed "concerns about possible provocations by Ukraine with the use of a 'dirty bomb'", Moscow said, reffing to a weapon that uses traditional explosives to scatter radioactive material.

Shoigu also spoke to Pentagon chief Lloyd Austin, but Moscow did not mention the dirty bomb allegations in its statement summarizing that call.

But Ukrainian President Volodymyr Zelensky reacted swiftly, calling for a united international response.

"If Russia calls and says that Ukraine is allegedly preparing something, it means one thing: Russia has already prepared all this," Zelensky said in a video address on social media.

"I believe that now the world should react as harshly as possible."

Earlier Sunday, Ukraine's Foreign Minister Dmytro Kuleba denounced Moscow's claims as "absurd" and "dangerous".

"Russians often accuse others of what they plan themselves," he added.

A British defence ministry statement said Defence Secretary Ben Wallace had "refuted these claims and cautioned that such allegations should not be used as a pretext for greater escalation".

And in Washington, National Security Council spokeswoman Adrienne Watson said Joe Biden's administration dismissed Moscow's "transparently false allegations that Ukraine is preparing to use a dirty bomb on its own territory."

Watson added: "The world would see through any attempt to use this allegation as a pretext for escalation."

'Vile strikes'

Russia also announced Sunday it had destroyed a depot in central Ukraine storing over 100,000 tonnes of aviation fuel.

Kyiv's energy operator meanwhile said scheduled power cuts had been introduced in the capital due to Russia's repeated strikes on Ukraine's power network and urged residents to use electricity sparingly.

More than one million Ukrainian households have lost electricity following recent Russian strikes and at least a third of the country's power stations having been destroyed ahead of winter, according to officials in Kyiv.

Zelensky condemned the strikes as "vile".

'Save your strength'

In the southern Ukrainian city of Kryvyi Rig, deputy mayor Sergiy Miliutin was dealing with emergencies and outages from his underground bunker, used as a venue for a children's martial arts competition.

"I've reached a point where I just survive on my drive. You have to stay level-headed and save your strength. No one knows how long this will all last," he told AFP.

The intensification of Russian strikes on Ukraine, particularly energy facilities, came after the bridge linking the annexed Crimea peninsula to mainland Russia was partially destroyed by an explosion earlier this month.

It was another major setback for Moscow's forces, battling to contain a Ukrainian counteroffensive in the south and east of the country.

Speaking in Rome on Sunday at the start of a peace conference, French President Emmanuel Macron said that it was for Ukrainians to decide when "peace is possible".

Ukraine reported three deaths in an overnight Russian artillery strike in the Toretsk area, a governor of the eastern Donetsk region said.

Inside Russia, two lines of defence have been built in the border region of Kursk to deal with any possible attack, a local governor said Sunday.

And defence structures are also being built in the neighbouring Russian border region of Belgorod after two civilians were killed there in strikes Saturday and thousands were left without electricity, according to governor Vyacheslav Gladkov.

Kherson evacuations

Meanwhile Ukraine's SBU intelligence service said it had detained two officials of Ukrainian aircraft engine maker Motor Sich on suspicion of working with Russia.

The SBU said management at the company's plant in Ukraine's southern Zaporizhzhia region -- partly controlled by Russian forces -- had colluded with Russian state-owned defence conglomerate Rostec.

The suspects had supplied Russia with Ukrainian aircraft engines that were used to make and repair attack helicopters, the SBU said.

In the southern Ukrainian region of Kherson, which Russia claims to have annexed, pro-Moscow officials have urged residents to leave amid Ukraine's counteroffensive.

Kherson, the region's main city, was the first to fall to Moscow's troops in the invasion's early days and retaking it would be a major prize for Kyiv.

Around 25,000 people have already left Kherson city to the left bank of the Dnipro River, according to Kremlin-installed officials.

Ukraine has denounced the removal of residents from Kherson, describing them as "deportations".