Russia lost a third of its strategic bombers as talks stalled, while Moscow’s forces made marginal advances on the front lines.

Ukraine has destroyed Russian strategic bombers in an unprecedented undercover drone operation while Russia launched its biggest-yet air raid on Ukraine’s cities and intensified attacks on its northern region of Sumy, when the two sides met for peace talks in Istanbul.

The two respective drone operations were emblematic of how direct peace talks, which began on May 15, have not abated the intensity of the conflict and may have deepened it.

Russian President Vladimir Putin has reportedly pledged a response.

Russia’s drone-and-missile attack on Saturday night involved 472 Shahed kamikaze drones, four cruise missiles and three ballistic missiles. Ukraine neutralised 385 aerial targets, its air force said, including three of the cruise missiles.