In the north a 50,000-strong Russian force is attacking Sumy, a provincial capital. Our model is detecting artillery fire and explosions along the city’s northern defensive lines. Ukraine is badly outnumbered but officials say the front is holding.

Hundreds of Russian drones and more than a dozen missiles rained down on the Ukrainian capital early on Thursday.

Kyiv was the main target of an hourslong assault that killed at least two people, officials said. The barrage came hours before the top American and Russian diplomats met.