Ukraine claimed to have launched a massive drone assault targeting dozens of Russian long-range bomber aircraft across the country. Governors in several Russian regions confirmed Ukrainian drone sightings, though it was unclear if any aircraft were hit.

The reported attack on June 1 came as a Russian missile hit a Ukrainian training base overnight, killing at least 12 troops and wounded dozens others, Ukrainian officials said.

The attacks by both sides come as negotiators from Kyiv and Moscow prepare for a second round of peace talks scheduled for June 2 in Istanbul.

The first round of talks last month ended with little tangible progress, although the two sides agreed to exchange hundreds of prisoners of war.

The Security Service of Ukraine, the country's main intelligence agency, released video on June 1 that it said showed drones hitting Russian strategic bombers at several bases. Bombers have played a key role in Russia's war, firing long-range cruise missiles at Ukrainian targets well out of range of Ukrainian air defenses.

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Air bases in the northern Murmansk and central Ryazan regions were reportedly hit, as was a base in the Siberian region of Irkutsk, which is more than 5,200 kilometers east of the Ukrainian border.

Governor Igor Kobzeva said it was the first time a Ukrainian drone had been spotted in the region.

In comments to RFE/RL's Ukrainian Service, unnamed officials with the agency, which is known as the SBU, claimed as many as 40 bombers may have been hit. SBU video appeared to show drones exploding into Tupolev bombers parked on tarmacs, while other video showed plumes of smoke rising over several bases.

There was no independent confirmation that any bombers had been damaged, thoughseveral Telegram channelswithlinks to Russia military sourcesreported four air bases in all had been targeted.

Ukraine's Ground Forces command,meanwhile, said a Russia missile hit the training ground just after midnight on June 1. Aside from the dead, more than 60 soldiers were wounded.

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The statement emphasized that there had been no gatherings of soldiers at the time of the attack. Russian forces in the past have targeted Ukrainian units gathering for ceremonies or unit muster, for example, prompting criticism from higher commanders

The attacks come with Russian and Ukrainian negotiators slated to meet in Istanbul on June 2 to try and hammer out a cease-fire or a wider peace deal.

Russia's tempo of operations has picked up in recent weeks, and Ukrainian authorities have warned that Russia could be preparing a new offensive.

Ukrainian President Volodymyr Zelenskyy said last week that Russia had amassed some 50,000 troops across the border from Ukraine's Sumy region. Officials have issued evacuation orders for scores of settlements in the region.