New Delhi, Dec. 10 -- U.S. President Donald Trump has unleashed the most extensive diplomatic effort to end the fighting in Ukraine since Russia's full-scale invasion nearly four years ago, but Washington's efforts have run into sharply conflicting demands by Moscow and Kyiv.

Ukrainian President Volodymyr Zelenskyy is set to meet Monday with European allies as he faces U.S. pressure to accept a plan to end the war at a time when Russian forces are making slow but steady gains.

Trump's special envoy Steve Witkoff and his son-in-law Jared Kushner visited Moscow last week for five-hour talks with Russian President Vladimir Putin. Witkoff and Kushner then held several meetings with senior Ukrainian officials in Florida in an attempt to iron...