Russia has denied aircraft were damaged and said explosions at the base on Tuesday were accidental

Satellite pictures released on Thursday showed devastation at a Russian air base in Crimea, hit in an attack that suggested Kyiv may have obtained new long-range strike capability with potential to change the course of the war.

Images from independent satellite firm Planet Labs showed three near-identical craters where buildings at Russia's Saki air base had been struck with apparent precision. The base, on the southwest coast of Crimea, suffered extensive fire damage with the burnt-out husks of at least eight destroyed warplanes clearly visible.

Russia has denied aircraft were damaged and said explosions at the base on Tuesday were accidental. Ukraine has not publicly claimed responsibility for the attack or said exactly how it was carried out.

Separately, the two sides accused each other of shelling the Zaporizhzhia nuclear power plant on Thursday, days after trading identical accusations that raised international concerns that the deployment of weapons there risked triggering a catastrophe.

U.N. Secretary-General Antonio Guterres early on Thursday called on both sides to halt all fighting near the plant - Europe's largest - held by Russian troops and operated by Ukrainian workers and near the front line in the fighting.

Ukraine's interior minister said Ukraine had to be ready for any scenario at the plant, including evacuating people.

"It's difficult to even imagine the scale of the tragedy which could come into effect if Russians continue their actions there," Denys Monastyrsky told Reuters.

Ukraine's Energoatom said the complex was struck five times on Thursday, including near where radioactive materials are stored, but nobody was injured and radiation levels remained normal. Russian-appointed local officials said Ukraine shelled the plant twice, disrupting a shift changeover, Russia's TASS news agency said.

Referring to the damage at Crimea's Saki air base, Ukrainian presidential adviser Mykhailo Podolyak said there were "numerous scenarios for what might have happened."

"Officially, we are not confirming or denying anything... bearing in mind that there were several epicentres of explosions at exactly the same time," he told Reuters in a message.

Western military experts said the scale of the damage and the apparent precision of the strike suggested a powerful new capability with potentially important implications. Russia, which seized and annexed Crimea in 2014, uses the peninsula as the base for its Black Sea fleet and as the main supply route for its invasion forces occupying southern Ukraine, where Kyiv is planning a counter-offensive in coming weeks.

The Institute for the Study of War think tank said Ukrainian officials were framing the Crimea strike as the start of Ukraine's counteroffensive in the south, suggesting intense fighting to come in August and September that could decide the outcome of the next phase of the war.

Exactly how the attack was carried out remains a mystery but the near-identical impact craters and simultaneous explosions appear to indicate it was hit by a volley of weapons capable of evading Russian defences.

The base is well beyond the range of advanced rockets that Western countries acknowledge sending to Ukraine so far, though within range of more powerful versions Kyiv has sought. Ukraine also has anti-ship missiles which could theoretically be used to hit targets on land.

Ukrainian Brigadier General Oleksiy Hromov, said Russia had doubled its air strikes on Ukrainian positions since last week, but that the intensity of Russian airborne activity in the south had reduced after the destruction at the Crimean base.

Russia captured territory in the east in huge battles that killed thousands of troops on both sides in June.

Since then front lines have been largely static, but Kyiv says it is preparing a big push to recapture the southern Kherson and Zaporizhzhia regions, the main slice of territory captured since the Feb. 24 invasion that Moscow still holds.

Kyiv hopes the arrival last month of U.S. rocket systems capable of hitting logistics targets behind the front line could tip the balance in its favour. But so far the West had held off on providing longer-range rockets that could strike deep in Russia itself or hit Moscow's many bases in annexed Crimea.

Russia says its "special military operation" is going to plan, to protect Russian speakers and separatists in the south and east. Ukraine and its Western allies say Moscow aims to solidify its grip on as much territory as possible.

Since the war started, tens of thousands of people have died, millions have fled, and cities have been destroyed.

Ukraine reported Russian bombardment along the entire front line, from the area around Kharkiv in the northeast, across eastern Donetsk province, and on the banks of the wide Dnipro river in Zaporizhzhia, Kherson and adjacent provinces.

"They mostly attack civilians. So they complain, protest. So they get tired from the war and turn their faces towards Russia. That's it," said Kharkiv resident Anatolii Tymchenko, as he looked at the wreckage of cars damaged in shelling and apartment blocks with blown out windows.

"People live here, it's usually very quiet, no military objects nearby. I have no idea why our yard was shelled," added resident Olena Ostapets.