On the eve of peace talks, Ukraine and Russia have ramped up the war with one of the biggest drone battles of the conflict, a Russian highway bridge blown up over a passenger train and an attack on nuclear-capable bombers deep in Siberia.
After days of uncertainty over whether Ukraine would even attend, President Volodymyr Zelenskiy said Defence Minister Rustem Umerov would meet Russian officials at the second round of direct peace talks in Istanbul on Monday.
The first round of the talks more than a week ago yielded the biggest prisoner exchange of the war - but no sense of any consensus on how to halt the fighting.
Amid talk of peace, though, there was much war.
At least seven people were killed and 69 injured when a highway bridge in Russia's Bryansk region, neighbouring Ukraine, was blown up over a passenger train heading to Moscow with 388 people on board. No one has claimed responsibility.
Ukraine attacked Russian nuclear-capable long-range bombers at a military base deep in Siberia on Sunday, a Ukrainian intelligence official said, the first such attack so far from the front lines more than 4300km away.
Ukraine's domestic intelligence service, the SBU, acknowledged it carried out the attack, codenamed "Operation Spider's Web", planned for more than a year and a half.
The intelligence official said the operation involved hiding explosive-laden drones inside the roofs of wooden sheds and loading them onto trucks that were driven to the perimeter of the air bases.
A total of 41 Russian warplanes were hit, the official said.
The SBU estimated the damage at $US7 billion ($A11 billion) and said Russia had lost 34 per cent of its strategic cruise missile carriers at its main airfields.
Zelenskiy expressed delight at the "absolutely brilliant outcome," and noted 117 drones had been used in the attack.
"And an outcome produced by Ukraine independently," he wrote.
"This is our longest-range operation."
Russia's Defence Ministry acknowledged that Ukraine launched drone strikes against Russian military airfields across five regions on Sunday.
Air attacks were repelled in all but two regions — Murmansk in the far north and Irkutsk in Siberia - where "the launch of FPV drones from an area in close proximity to airfields resulted in several aircraft catching fire".
Russia launched 472 drones at Ukraine overnight, Ukraine's air force said, the highest nightly total of the war. Russia also launched seven missiles.
Russia reported new drone attacks, listing 53 attacks intercepted in a period of less than two hours, including 34 over the border Kursk region.
Russia said it had advanced deeper into the Sumy region of Ukraine, and open source pro-Ukrainian maps showed Russia took 450sq/km of Ukrainian land in May, its fastest monthly advance in at least six months.
According to US envoy Keith Kellogg, the two sides will present their respective documents outlining their ideas for peace terms, though it is clear that after three years of intense war, Moscow and Kyiv remain far apart.
Russia's lead negotiator, presidential adviser Vladimir Medinsky, was quoted by TASS news agency as saying the Russian side had received a memorandum from Ukraine on a settlement.
According to a copy of the Ukrainian document seen by Reuters with a proposed roadmap for a lasting peace, there will be no restrictions on Ukraine's military strength after a deal is struck.
Nor will there be international recognition of Russian sovereignty over parts of Ukraine taken by Moscow's forces and reparations for Ukraine.