Ukraine's gas facilities have suffered severe damage from Russian drone and missile attacks, forcing the country to import more gas

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.

Nov. 25 (UPI) -- At least six people were killed by Russia in an overnight attack on Kyiv, the city's mayor said Tuesday, as the United States and Ukraine held talks over the weekend to finalize a peace plan.

Certainly, the latest rounds of American bargaining and pressure on Ukraine are the most substantial yet. “This isn’t another round of what we saw before,” says a Western diplomat in Kyiv. Those close to the talks speak of “serious progress” bringing some Ukrainian and Russian positions together.

As President Trump pushes for peace, Ukraine's growing manpower crisis spells new uncertainties on the battlefield and the negotiating table.

U.S. and Ukrainian officials sought to narrow the gaps between them on Monday over a plan to end the war in Ukraine, after agreeing to modify a U.S. proposal that Kyiv and its European allies saw as a Kremlin wish list.

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.

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,

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.

The update was issued hours after Russia launched a wave of overnight attacks on Ukraine's capital, Kyiv, with at least seven people killed in strikes that hit city buildings and energy infrastructure.

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

The meeting last week was just the latest example of a long-running rift inside the Trump administration over how to end the war in Ukraine.