(Reuters) -A Russian drone hit a bus carrying workers in the Ukrainian city of Marhanets on Wednesday, killing nine people and injuring close to 50, Kyiv officials said, in an attack President Volodymyr Zelenskiy said was a "deliberate war crime".

Zelenskiy said the Russian strike hit a bus that was transporting workers of a mining and processing plant.

"An ordinary bus. Clearly a civilian object, a civilian target," Zelenskiy said on X.

"It was an egregiously brutal attack – and an absolutely deliberate war crime," he added, calling for "an immediate, full, and unconditional ceasefire".

Russia fired a total of 134 attack drones at targets in Ukraine overnight, Kyiv's air force said. There was no immediate comment from Russia.

Ukrainian officials arrived in London on Wednesday, even as most other big power foreign ministers pulled out, to hold talks about ways to achieve a ceasefire as a first step towards peace.

Marhanets, in south-central Ukraine, lies on the Ukrainian-controlled north bank of the Dnipro river's dried-up reservoir that separates the warring sides.

Dnipropetrovsk regional governor Serhiy Lysak said nine people were killed in the attack and 49 were injured.

Zelenskiy shared photographs of the aftermath of the attack on X, showing bodies lying in and next to the bus and being carried away by emergency workers.

Zelenskiy added most of the injured were women.

Elsewhere, an energy plant that provides electricity to the city of Kherson near southern front lines was destroyed in an artillery and drone attack, regional governor Oleksandr Prokudin said.

Ukraine's emergency service also reported a drone strike on the Synelnykivskyi district in the Dnipropetrovsk region that injured two people and sparked a fire at an agricultural enterprise.

Russia further fired drones into the central region of Poltava, injuring at least six people, its governor said.

A drone attack on civilian infrastructure in the suburbs of the Black Sea port city of Odesa injured two people and sparked several fires, regional governor Oleh Kiper said on Telegram. 

Russian drone salvoes also set off large-scale fires in Ukraine's second largest city, Kharkiv, in the northeast, Mayor Ihor Terekhov said on Telegram. 

Seven private houses, a storage building and an outbuilding were also damaged by drones hitting the Kyiv capital region, where a fire also broke out in a restaurant complex, its regional governor said.

Both Russia and Ukraine are under pressure from the United States to demonstrate progress towards ending the war that began with Russia's 2022 full-blown invasion amid warnings that U.S. President Donald Trump could walk away from peacemaking.

(Reporting by Lidia Kelly in Melbourne and Anna Pruchnicka in Gdansk; Editing by Chris Reese, Gerry Doyle and Ros Russell)