The operator of Ukraine’s nuclear plants says it faced an ambitious cyberattack.

Washington – The operator of Ukraine’s nuclear plants says it faced an ambitious cyberattack.

The Ukrainian energy agency responsible for the oversight and safe operation of the nation’s nuclear power plants said on Tuesday night that Russian hackers had launched their most ambitious effort yet on the company’s official website.

The attack appeared to fail and there was no indication that it threatened to disrupt the Ukrainian power grid or the company’s oversight of the nation’s 15 working nuclear reactors.

Ukraine’s power grid has been knocked offline twice before, in 2015 and 2016, causing widespread blackouts, and Russian efforts to attack the Energoatom site were being closely watched in case they presaged a larger event.

The large-scale cyberattacks — like knocking out Ukraine’s power grid or frying cellular service — that Western intelligence officials worried would accompany the Russian invasion in February have failed to materialize.

But Russia has used hacking campaigns to support its ground campaign, pairing malware with missiles in several attacks, including on TV stations and government agencies, according to a report released in April by Microsoft.

It remains unclear who is to blame for the shelling. The Ukrainians have accused the Russians of directing strikes there to cut off energy supplies to other cities, while the Russians say Ukraine is responsible for the attacks.

On Tuesday, President Emmanuel Macron of France and President Volodymyr Zelensky of Ukraine spoke by telephone about safety threats at the Zaporizhzhia plant.

According to a statement from Mr. Macron’s office, the French president stressed his concern about the “ongoing clashes on the safety and security of Ukrainian nuclear facilities” and called for the withdrawal of Russian forces.