Ukraine denounced what it called "fake elections" being held by Moscow on its occupied territory Friday, while Russian air strikes across the country killed four people and wounded dozens more.

Russia said voting for local officials was open in the four Ukrainian regions of Donetsk, Lugansk, Zaporizhzhia and Kherson -- none of which Moscow fully controls -- as well as in Crimea.

"Russia's pseudo-elections in the temporarily occupied territories are worthless," Ukraine's foreign ministry said in a statement, accusing Moscow of "grossly violating" its sovereignty.

The votes came as Russia continued to pound Ukrainian cities in the centre and east of the country with air strikes, as Kyiv officials posted images of the destruction on social media.

"A Russian aerial bomb killed three civilians in Odradokamyanka -- two women and a man. Four local residents were injured," Interior Minister Igor Klymenko said, calling the attack a "war crime".

Odradokamyanka is about 60 kilometres (40 miles) upstream of Kherson city, on the west bank of the Dnipro river, which was recaptured by Ukraine's forces last year.

A Russian strike on President Volodymyr Zelensky's hometown of Kryvyi Rig killed a policeman, Klymenko said, after a police building in the city centre was hit.

Photos from the scene showed smoke spewing from the ruins of the building as rescue workers carried an injured person to an ambulance.

"Rescuers of the State Emergency Service pulled out three more from under the rubble. They are in serious condition," he said.

Russia also struck the city of Sumy in northeast Ukraine, officials said, while one man was injured by a rocket attack on Zaporizhzhia in the southeast.

- "Extraordinary resilience" -

The new wave of strikes on Ukraine came a day after top US diplomat Antony Blinken wrapped up his surprise two-day visit, in which he announced $1 billion of new wartime aid and praised Kyiv's "extraordinary resilience".

"President Biden asked me to come to reaffirm strongly our support, to ensure that we are maximising the efforts that we're making," Secretary of State Blinken told Zelensky on Wednesday.

The United States has provided Ukraine with over $40 billion of security assistance since Russia invaded last year, including weapons Kyiv says are vital to pushing back Russian forces.

Ukraine, which had for months been pressing for more Western help, launched a counteroffensive against Russian forces in June after building up assault battalions and stockpiling Western weapons.

Progress has been slow however, as Kyiv's forces encounter waves of heavily fortified Russian defences.

Washington promised this week to supply Kyiv with depleted-uranium tank rounds to boost Ukraine's firepower, a decision the Kremlin warned was "very bad news".

"The use of these shells has resulted in a galloping increase in the number of cancer patients ... The same situation will inevitably await those Ukrainian territories where they will be used," Kremlin spokesman Dmitry Peskov said Thursday.

- "Ukrainian agents" -

On Friday, Russia's FSB security services said they had detained a man on suspicion of plotting to bomb a railway in Crimea, as the region's Moscow-installed governor said air defences had shot down a drone.

Crimea, which Russia seized from Ukraine in 2014, has been repeatedly targeted by Ukrainian drone strikes and sabotage attacks as Kyiv tries to retake the peninsula.

The FSB said the suspect -- a Russian citizen in his mid-40s -- had been "collecting information on the deployment of Russian defence ministry facilities and units" and was preparing a railway bombing.

"In а hiding place he had organised (we) found and seized an improvised explosive device made using foreign-made plastic explosives," it said.

It said the man had been acting on the "instructions of Ukrainian military intelligence" and had been remanded in custody.

The Russian-appointed governor of Crimea, Sergei Aksyonov, warned that transport infrastructure had become a main target for "terrorism" and that Ukrainian saboteurs would be punished.

"An unenviable fate awaits the Ukrainian agents. They will be found and punished," he said.

He later said a Ukrainian drone had been shot down over the north of the peninsula, but did not report any further details.

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