As peace talks between Russia and Ukraine resumed, the Kremlin accused the Ukrainians of launching a helicopter attack on a fuel depot on Russian soil. Ukraine denied responsibility for the blast, but, if Moscow’s claim is confirmed, it would be the war’s first known attack in which Ukrainian aircraft penetrated Russian airspace. Russia has reported cross-border shelling from Ukraine before, including an incident last week that killed a military chaplain, but not an incursion of its airspace.

Russian Defense Ministry spokesman Igor Konashenkov said two Ukrainian helicopter gunships flew in extremely low and attacked the civilian oil storage facility on the outskirts of the city of Belgorod, about 25 kilometres from the Ukraine border. The regional governor said two workers at the depot were wounded, but the Rosneft state oil company denied anyone was hurt. “Certainly, this is not something that can be perceived as creating comfortable conditions for the continuation of the talks,” Kremlin spokesman Dmitry Peskov said, five weeks after Moscow began sending upwards of 1,50,000 of its own troops across Ukraine’s border.

The latest negotiations took place by video. At a round of talks earlier in the week, Ukraine said it would be willing to abandon a bid to join NATO and declare itself neutral  Moscow’s chief demand  in return for security guarantees from several other countries. The invasion has left thousands dead and driven more than 4 million refugees from Ukraine.

Mariupol, the shattered and besieged southern port city, has seen some of the worst suffering of the war. Its capture would be a major prize for Russian President Vladimir Putin, giving his country an unbroken land bridge to Crimea, seized from Ukraine in 2014.

-Inputs from agencies