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.

Ukraine's top military commander Oleksandr Syrskyi warned on Saturday of a possible new Russian offensive in the Kharkiv region, a part of northeastern Ukraine which has seen heavy fighting since Russia invaded in 2022.

U.S. President Donald Trump has voiced frustration with Russian President Vladimir Putin over the intensification of attacks.