As Washington ramps up its negotiations with Ukraine and Russia and U.S. President Donald Trump expresses optimism that a peace deal could be close, there are still some very critical and contentious issues on which Kyiv and Moscow are in deep disagreement.

The U.S. and Kyiv agreed in a joint statement that a final peace deal “must fully uphold Ukraine’s sovereignty and deliver a sustainable and just peace.” But neither side explained how the revised plan differed from the original,

The Trump administration’s Army secretary will sit down Tuesday with Russian officials in Abu Dhabi to present a slimmed-down plan to end Moscow’s 33-month-old invasion of Ukraine.

US Army Secretary Dan Driscoll held meetings with Russian officials in Abu Dhabi on Monday about a proposed plan for ending the war in Ukraine, with talks to continue Tuesday, a US official told CNN.

ABC News’ Ian Pannel reports from Kyiv as fresh attacks hit while a 19-point peace plan is considered in Switzerland.

Russia launched a large-scale attack on Ukraine on Tuesday, as American and Russian officials held talks in Abu Dhabi about President Donald Trump’s peace plan and Ukraine indicated that President Volodymyr Zelenskyy was prepared to go to Washington to finalize a deal.

President Donald Trump on Tuesday directed Special Envoy Steve Witkoff to travel to Moscow for talks with Russian President Vladimir Putin.

A large-scale Russian aerial barrage on the Ukrainian capital killed at least six people on Tuesday. The attack came hours after a round of peace talks between U.S. and Ukrainian mediators that ended in Geneva.