Russian forces have ratcheted up attacks on Ukrainian railway infrastructure with the aim of disrupting military cargo ahead of a planned offensive, a Ukrainian security source said Friday.

Russian forces have firepower and manpower advantages across the front line in Ukraine and Kyiv has warned that fighting will become increasingly difficult in the coming weeks.

The uptick in deadly Russian attacks is intended to destroy train facilities and "paralyse deliveries and movement of military cargo" as Moscow prepares to advance, the source said.

"These are standard steps ahead of an offensive," it added.

President Volodymyr Zelensky has warned that the Kremlin wants its army to capture the strategic heights of Chasiv Yar, a village in the eastern Donetsk region, before May 9.

That is when Russia celebrates the Soviet Union's victory over Nazi Germany in World War II. The Kremlin claims to have annexed the Donetsk region.

Regional officials and Ukrainian railway operator Ukrzaliznytsia have reported an uptick in deadly strikes on railway facilities, including in Donetsk.

Three railway employees were killed and four more were wounded, the company said, during a Russian missile attack on the region Thursday.

Ten civilians were also wounded on Thursday when Russian forces attacked railway facilities in Balakliya in the Kharkiv region.

The Russian defence ministry said Friday that a strike on Udachne in the Donetsk region had targeted what it said were "Western weapons and military equipment" being transported by railway.

It said it had also struck railway loading facilities at Balakliya.

Those strikes however represent just a small number of the attacks that have damaged trains or stations across Ukraine, including in more central regions, like Cherkasy and Dnipro.

Oleksandr Pertsovsky, the head of passenger transportation at Ukrzaliznytsia, confirmed to AFP that there had been more strikes on railway facilities.

"Our employees are at risk, because when repair work is ongoing, unfortunately, there are often repeat hits," he said.

"We see strikes related to railway logistics, and they hit mostly civilian facilities. They're hitting the stations indiscriminately. It's a very primitive way of doing it," he added.

Ukrzaliznytsia was established after the collapse of the Soviet Union and operates some 22,000 kilometres of rail networks across the country.

One of the deadliest attacks of the war occurred in April 2022 when Russian forces struck the railway station in Kramatorsk killing more than 60 people trying to flee Russia's advance.