Russian soldiers were snug in their sleeping bags, sleeping off a hard day of combat in a building presumably somewhere along the front line in eastern Ukraine when their slumber was interrupted. An explosive first-person-view drone operated by the elite Birds of Magyar unit slipped into the building—and struck the snoozing Russians,

The assault underscored the deep mistrust between Russia and Ukraine as U.S.-mediated talks about a partial cease-fire began in Saudi Arabia.