Russia launched almost 500 drones at Ukraine in the biggest overnight drone bombardment of the three-year war, the Ukrainian air force said Monday, as the Kremlin presses its summer offensive amid direct peace talks that have yet to deliver progress on stopping the fighting.

Moscow’s dual campaign of intensified frontline attacks and bombardment of Ukrainian cities has further reduced the prospects for an end to the fighting.

The warring sides also exchanged prisoners in one of the few results of talks last week, and Russia reported new attacks on the front line.