It is highly unusual for the top diplomat of the United States, the linchpin of the transatlantic alliance, to skip the annual December meeting -- and even more striking as the agenda is set to be dominated by discussions about the intensive US diplomacy on the war in Ukraine.

People familiar with Rubio's travel plans, speaking on condition of anonymity, said that at this point he was not planning to attend the meeting in Brussels next Wednesday and Thursday and would instead send his deputy, Christopher Landau.

Also next week, as Rubio stays away from the NATO talks, President Donald Trump's envoy Steve Witkoff is expected in Moscow to discuss Ukraine diplomacy.

Rubio traveled last weekend to Switzerland for talks with Ukraine on a plan to end the war that has been criticized by European allies as looking like a wishlist for Moscow, which invaded Ukraine in February 2022.

Rubio also met European national security advisors in Geneva.

A senior State Department official insisted that the Trump administration has already made progress in NATO by pressing allies to step up defense spending.

"Secretary Rubio has already attended dozens of meetings with NATO allies and it would be completely impractical to expect him at every meeting," the official said on condition of anonymity.

"The historic foreign policy achievements in just 10 months of this administration speak for themselves," the official said.

Washington's original plan -- drafted without input from Ukraine's European allies -- would have seen Kyiv withdraw from its eastern Donetsk region and the United States de facto recognize the Donetsk, Crimea and Lugansk regions as Russian.

Washington pared back the original plan following criticism from Kyiv and Europe, but the current contents remain unclear.

Throwing additional uncerainty on the diplomacy, Ukraine's top negotiator Andriy Yermak was removed Friday by President Volodymyr Zelensky as his aide came under a corruption probe.