“They’re going to continue to have American support for the defense of their territory for defeating Russian aggression,” John Kirby, strategic communications coordinator for the National Security Council, told CNN Friday.

Equally surprising, officials said, is the Kremlin’s slow response to the incursion, the first time Russia has lost sovereign territory since invading Ukraine more than two years ago.

Russia appears to have diverted at least several thousand troops away from front-line fighting in occupied Ukraine in order to address the territorial loss in the Kursk region. One US official said Russia will likely end up having to send more troops to the area to strengthen its own defenses, as the US watches to see where Russia will find the manpower.

Meanwhile, senior US officials have tried to gain a better understanding of Kyiv’s goal in carrying out the offensive into Russia. Ukraine did not inform the US in advance of the incursion, and the US is still not clear on what the long-term goal is for the operation.

On Friday, an aide to Ukrainian President Volodymyr Zelensky said the cross-border incursion is aimed at creating a “fair negotiation process” and inflicting “significant tactical defeats” on Russia.

“Negative changes in the psychological state of the Russian population will be another argument for the start of negotiations,” said Mykhailo Podolyak, adviser to the Head of the Office of the President of Ukraine, on social media.

Russia’s reaction may be delayed, officials said, but there is little doubt that a response is coming. Ukraine says it has seized approximately 400 square miles of territory inside Russia, forcing Russian authorities to declare emergencies and carry out large-scale evacuations.

US Defense Secretary Lloyd Austin spoke with his Ukrainian counterpart, Rustem Umerov, Wednesday and tried to learn more about the objectives of the offensive, launched nearly two weeks ago.

“Throughout the department, we are engaging with the Ukrainians trying to get a better understanding of their objectives,” said deputy Pentagon press secretary Sabrina Singh.

Pressed on whether Austin told Umerov that he supports the operation, Singh demurred.

“What I can tell you is where we are supportive and that is Ukraine continuing to defend itself,” she said.