Satellite pictures released on Thursday showed devastation at a Russian air base in Crimea, hit days earlier in an attack that suggested Kyiv may have obtained new long-range strike capability with potential to change the course of the war.
Pictures released by independent satellite firm Planet Labs showed three near-identical craters that had precisely struck buildings at Russia's Saki air base. The base, on the southwest coast of Crimea had 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 seen at the base on Tuesday were accidental.
Ukraine has not publicly claimed responsibility for the attack or said exactly how it was carried out.
"Officially, we are not confirming or denying anything; there are numerous scenarios for what might have happened... bearing in mind that there were several epicentres of explosions at exactly the same time," Ukrainian presidential adviser Mykhailo Podolyak 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 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.
"I'm not an intel analyst, but it doesn't look good," Mark Hertling, a former commander of U.S. ground forces in Europe, wrote on Twitter, linking to an image of the devastation at the Russian base.
"I am. It's very good," replied his fellow retired four-star American general, Michael Hayden, former head of the CIA and National Security Agency.
Exactly how the attack was carried out remains a mystery. Some Ukrainian officials have been quoted suggesting it may have been sabotage by infiltrators. But the near identical impact craters and simultaneous explosions appear to indicate it was hit by a volley of new long-range 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, but within the range of more powerful versions that Kyiv has sought. Ukraine also has its own surface-to-ship missiles which could theoretically be used to hit targets on land.
The war in Ukraine is expected to enter a new phase in coming weeks. Ukraine drove Russian forces back from the capital Kyiv in March and from the outskirts of the second-largest city Kharkiv in May. Russia captured more 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 regions of Kherson and Zaporizhzhia, the main slice of territory captured since the Feb. 24 invasion held by Moscow.
Russia has reinforced those regions, but its defence depends on being able to control supply lines to stock its troops with the thousands of shells a day that its artillery-heavy forces are accustomed to firing.
Kyiv hopes the arrival last month of U.S. rocket systems capable of hitting Russian 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 in the south and east, where it recognises separatists as independent. Ukraine and its Western allies say the invasion failed in an initial bid to overthrow the government in Kyiv, and Moscow now aims to solidify its grip on as much territory as possible with the ultimate goal of extinguishing Ukraine as an independent nation.
Tens of thousands of people have died, millions have fled and cities have been destroyed since Russia invaded on Feb. 24.
Although there have been few major advances on either side in recent weeks intense skirmishes are still under way.
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.
Dnipropetrovsk regional governor Valentyn Reznychenko said three people were killed and seven wounded by shelling in Nikopol on the right bank of the Dnipro, which was hit by 120 Grad rockets.
"The enemy is concentrating its efforts on establishing full control over the territories of the Luhansk and Donetsk regions," Ukraine's General Staff said in an early Thursday report, citing more than 60 settlements and military targets.
Russian-backed separatists claimed to have captured Pisky, a small town on the outskirts of separatist-held Donetsk city, which has seen fighting in recent days.
"It's hot in Pisky. The town is ours but there remain scattered pockets of resistance in its north and west," separatist official Danil Bezsonov said on Telegram.
Ukrainian officials denied that the town had fallen. Reuters was unable to verify the battlefield accounts.
Oleksiy Arestovych, a Ukrainian presidential adviser, said in an interview posted on YouTube that Russian "movement into Pisky" had been "without success".
Ukraine accused Russia on Wednesday of killing at least 13 people and wounding 10 with rockets fired from the vicinity of Europe's largest nuclear power plant, in the knowledge it would be risky for Ukrainian forces to return fire.
"The cowardly Russians can't do anything more so they strike towns ignobly hiding at the Zaporizhzhia atomic power station," Andriy Yermak, President Volodymyr Zelenskiy's chief of staff, said on social media.
Ukraine says about 500 Russian troops are at the plant, where Ukrainian technicians continue to work. The Group of Seven major industrialised countries on Wednesday told Russia to hand back the plant to Ukraine, after the U.N. atomic energy watchdog sounded the alarm over the possibility of a nuclear disaster.
(Reporting by Reuters bureaux; Writing by Peter Graff; Editing by Hugh Lawson)