KYIV—Ukrainian President Volodymyr Zelensky said he would be willing to pull troops out of the eastern region of Donetsk and create a demilitarized free economic zone as part of a potential peace deal, provided Russia took similar steps to withdraw from areas it controls. Speaking to reporters on Tuesday, Zelensky said the proposal and other aspects of a 20-point plan would be put to a referendum. The territorial dispute across the Donbas, the eastern flank of Ukraine where some of the heaviest fighting is raging, is one of the chief sticking points in the latest version of a plan to...