Ukrainian President Volodymyr Zelensky said on Sunday that the country’s constitution makes it “impossible” to surrender any land to Russia, rejecting a proposal from President Vladimir Putin that Kyiv withdraw from the still-unoccupied portions of Donetsk Oblast in exchange for freezing hostilities along other parts of the front line in Kherson and Zaporizhzhia. The plan is understood to have the backing of U.S. President Donald Trump, who met Putin at a summit in Alaska last week and is scheduled to host Zelensky at the White House on Monday. Zelensky insisted that territorial issues could only be discussed at a trilateral meeting with both Washington and Moscow present and warned that additional sanctions on Russia would be necessary if the Kremlin refuses to engage. Allied governments are due to confer later on Sunday in a “coalition of volunteers” video call to consider security guarantees for Kyiv. Russia currently controls roughly 20% of Ukrainian territory, including most of Luhansk and significant parts of Donetsk, but has yet to seize the main urban centers of Zaporizhzhia and Kherson.