Small bands of Russian soldiers thrust deeper into eastern Ukraine on Tuesday before a summit between Russian President Vladimir Putin and U.S. President Donald Trump, which European leaders fear could end in peace terms imposed on an unlawfully shrunken Ukraine.

In one of the most extensive incursions so far this year, Russian troops advanced near the coal-mining town of Dobropillia, part of Putin's campaign to take full control of Ukraine's Donetsk region. Ukraine's military dispatched reserve troops, saying they were in difficult combat against Russian soldiers.

Trump has said any peace deal would involve "some swapping of territories to the betterment of both" Russia and Ukraine, which has up to now depended on the U.S. as its main arms supplier. But because all the areas being contested lie within Ukraine, President Volodymyr Zelenskyy and his European Union allies fear that he will face pressure to give up far more than Russia does.