The latest assault on Kyiv came as Ukrainian peace negotiators are due to meet their U.S. counterparts this weekend.

Russian President Vladimir Putin said that a US plan to end the war in Ukraine could “form the basis for future agreements” but renewed threats to seize more territory by force unless Kyiv withdraws.

Russian forces strafed Ukraine’s capital with a major missile barrage overnight, killing at least three people and causing widespread power outages, as the US ramps up pressure on President Volodymyr Zelenskiy to agree to concessions in the almost four-year-old war.

The two oil tankers, identified as the Kairos and Virat, were empty and sailing to Novorossiysk, a major Russian Black Sea oil terminal.

"None of us really know what Zelenskyy is like operating solo, because he never has," one expert told NBC News.

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

The assault came hours after President Zelensky announced the resignation of his chief of staff, also lead negotiator in talks with the US.

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.

Russian drone and missile attacks on Kyiv killed at least two people and wounded 15 Saturday, officials said, as renewed U.S.-led peace negotiations gathered momentum.

After working together during the successful presidential campaign of 2019, Yermak became Zelensky's chief of staff. He stood next to the president as he gave his now famous "we are still here" speech as the Russians descended on Kyiv at the start of their full-scale invasion in February 2022.