Ukraine’s surprise invasion of Russia’s Kursk region derailed landmark negotiations that may have led to a partial ceasefire agreement between the two warring nations.

In a major shift earlier in August, both sides had agreed to send delegations to the Qatari capital Doha for indirect talks to halt attacks on energy infrastructure, The Washington Post reported.

However, the Russian side postponed the meeting after Ukraine’s troops stormed into its territory on Aug 6. Moscow’s delegation described it as an “escalation”, an unnamed diplomat said.

Some officials had hoped the talks, which were set to be mediated by Qatari officials, would be the first step towards an agreement to end the war.

“After Kursk, the Russians balked,” another source familiar with the talks said.

Russia is yet to call off the negotiation entirely and Ukraine’s presidential office said that the Doha summit would still take place on Aug 22 via video link.

The two sides have not met in person since secret negotiations were held in Istanbul in the first months of the full-scale war in 2022. The talks eventually fell apart. In July that year, Russia and Ukrainian officials agreed on a Black Sea grain deal but that collapsed months after.

Other negotiations, including ones to establish humanitarian corridors, have largely failed.

However, an agreement to end costly attacks to energy infrastructure would be beneficial economically to both sides.

Ukraine has weathered Russian missile and drone hits on its power network since the first winter of the war, causing rolling blackouts that have significantly affected lives and local businesses.

Ukraine has retaliated by setting Russia’s oil facilities on fire with long-range drone attacks, reducing oil output by around 15 per cent and raising global gas prices.

The postponement of the talks has put added pressure on Ukraine’s incursion into Russia, which officials and experts believe was intended in part to give Ukraine more leverage in any future negotiations.

Kyiv claims to be in control of some 1,000 km (620 miles) of Russian land after launching its cross-border assault that has humiliated Moscow’s military and prompted Russia to evacuate about 200,000 civilians from border regions.

Military analysts have aired scepticism that Ukraine will be able to maintain the gains, while Russia continues to push forward in the Donetsk region of eastern Ukraine.

Moscow has previously demanded that Kyiv cede four of its regions – Donetsk, Luhansk, Zaporizhzhia and Kherson – to its control to end the war, including areas that are not occupied.

Volodymyr Zelensky, the Ukrainian president, has said that he would only consider a ceasefire if Russia withdrew all of its troops from Ukrainian land including the Crimean Peninsula which Moscow annexed in 2014.