“We have other targets on the territory of Ukraine,” he said, “I mean collaborationists and representatives of the Russian command, who might have value for members of our special services working in this program, but certainly not Dugina.”

Though details surrounding acts of sabotage in Russian-controlled territory have been shrouded in mystery, the Ukrainian government has quietly acknowledged killing Russian officials in Ukraine and sabotaging Russian arms factories and weapons depots.

A senior Ukrainian military official who declined to be identified because of the sensitivity of the topic, said that Ukrainian forces, with the help of local fighters, had carried out assassinations and attacks on accused Ukrainian collaborators and Russian officials in occupied Ukrainian territories. These include the Kremlin-installed head of the Kherson region, who was poisoned in August and had to be evacuated to Moscow for emergency treatment.

Countries traditionally do not discuss other nations’ covert actions, for fear of having their own operations revealed, but some American officials believe it is crucial to curb what they see as dangerous adventurism, particularly political assassinations.

Still, American officials in recent days have taken pains to insist that relations between the two governments remain strong. U.S. concerns about Ukraine’s aggressive covert operations inside Russia have not prompted any known changes in the provision of intelligence, military and diplomatic support to Mr. Zelensky’s government or to Ukraine’s security services.

In a phone call on Saturday, Secretary of State Antony J. Blinken told his Ukrainian counterpart, Dmytro Kuleba, that the Biden administration “will continue to support Ukraine’s efforts to regain control of its territory by strengthening its hand militarily and diplomatically,” according to Ned Price, the State Department’s spokesman.

Officials from the State Department, National Security Council, Pentagon and C.I.A. declined to comment on the intelligence assessment.