ISTANBUL, June 2, 2025 (AFP) - Russian and Ukrainian officials will meet Monday in Istanbul to exchange their plans for how to end the three-year war, Europe's largest conflict since World War II, after Kyiv says it struck dozens of strategic bombers parked at airbases deep in Russia.

Urged on by US President Donald Trump, Moscow and Kyiv have opened direct negotiations for the first time since the early weeks of Russia's invasion but have yet to make significant progress towards an elusive agreement.

Monday's talks come a day after Ukraine carried out one of its most brazen and successful attacks ever on Russian soil -- hitting dozens of strategic bombers parked at airbases thousands of kilometres behind the front line.

At the first round of talks in Istanbul last month, they agreed a large-scale prisoner exchange and to swap notes on what their vision of a peace deal might look like.

The second set of negotiations is scheduled to get underway at 1:00 pm (1000 GMT) at the Ciragan Palace in Istanbul, an Ottoman imperial house on the banks of the Bosphorus that is now a luxury five-star hotel.

Russia says it will present a "memorandum" of its peace terms, having resisted pressure by Ukraine to send its demands in advance.

Despite the flurry of diplomacy, the two sides remain far apart over a possible deal -- either for a truce or longer-term settlement.

Outlining Kyiv's position ahead of the talks, Ukrainian President Volodymyr Zelensky refreshed his call for an immediate halt to the fighting.

"First -- a full and unconditional ceasefire. Second -- the release of prisoners. Third -- the return of abducted children," he said Sunday in a post on social media.

He also called for the sides to discuss a direct meeting with Russian President Vladimir Putin.

"The key issues can only be resolved by the leaders," Zelensky said.

The Kremlin has repeatedly pushed back on that prospect, saying a Putin-Zelensky meeting could only happen after the negotiating delegations reach wider "agreements".

Russia has questioned Zelensky's legitimacy throughout the war and repeatedly called for him to be toppled.

Moscow says it wants to address the "root causes" of the conflict -- language typically used to refer to a mix of sweeping demands including limiting Ukraine's military, banning the country from joining NATO and massive territorial concessions.

Kyiv and the West have rejected those calls and cast Russia's assault as nothing but an imperialist land grab.

Tens of thousands have been killed since Russia invaded, with swathes of eastern and southern Ukraine destroyed and millions forced to flee their homes.

- War rages on -

Russia's top negotiator in Istanbul will be Vladimir Medinsky, an ideological Putin aide who led failed talks in 2022, has written school textbooks justifying the invasion and questioned Ukraine's right to exist.

Ukraine's team will be led by Defence Minister Rustem Umerov, seen as a skilled and pragmatic negotiator, but who has been mired in domestic scandal over alleged abuse of power and a lack of transparency.

"Diplomatic advisors" from Germany, France and Britain will be "on the ground... in close coordination with the Ukrainian negotiating team," a German government spokesperson said Sunday.

Ukraine on Sunday said it had damaged some 40 strategic Russian bombers, worth $7 billion, in a major special operation after months of setbacks for Kyiv's military.

Kyiv's security service said the plan, 18 months in the making, had involved smuggling drones into Russia which were then launched from near the airbases, thousands of kilometres away from the front lines.

Russian troops have meanwhile been advancing on the ground, particularly in the northeastern Sumy region, where Putin ordered his forces to establish a "buffer zone" along the border.

Ballistic strikes in the northeastern Kharkiv region on Monday injured at least six people, including a seven-year-old, and damaged a civilian business and a warehouse, Kharkiv Governor Oleg Synegubov said on Monday.

Ahead of the talks, Russian officials have called for Ukraine to be cut off from Western military support and cede territory still controlled by its army.

Ukraine has pushed Russia to agree a full, unconditional and immediate ceasefire -- saying a pause in the fighting is necessary to then discuss what a long-term settlement could look like.

Kyiv has refused to formally give up the one-fifth of its territory controlled by Russia, though it has accepted that it may only be able to get some land back through diplomacy, not fighting.

It also wants concrete Western-backed security guarantees -- like NATO protections or Western troops on the ground -- that have also been ruled out by Russia.