WASHINGTON >> U.S. intelligence agencies believe parts of the Ukrainian government authorized the car bomb attack near Moscow in August that killed Daria Dugina, daughter of a prominent Russian nationalist, an element of a covert campaign that U.S. officials fear could widen the conflict.

The United States took no part in the attack, either by providing intelligence or other assistance, officials said. U.S. officials also said they were not aware of the operation ahead of time and would have opposed the killing had they been consulted. Afterward, U.S. officials admonished Ukrainian officials over the assassination, they said.

The closely held assessment of Ukrainian complicity, which has not been previously reported, was shared within the U.S. government last week. Ukraine denied involvement in the killing immediately after the attack, and senior officials repeated those denials when asked about the U.S. intelligence assessment.

While Russia has not retaliated in a specific way for the assassination, the United States is concerned that such attacks — while high in symbolic value — have little direct effect on the battlefield and could provoke Moscow to carry out its own strikes against senior Ukrainian officials. U.S. officials have been frustrated with Ukraine’s lack of transparency about its military and covert plans, especially on Russian soil.

Since the beginning of the war, Ukraine’s security services have demonstrated their ability to reach into Russia to conduct sabotage operations. The killing of Dugina, however, would be one of the boldest operations to date — showing Ukraine can get very close to prominent Russians.

Some U.S. officials suspect Dugina’s father, Alexander Dugin, a Russian ultranationalist, was the actual target of the operation and that the operatives who carried it out believed he would be in the vehicle with his daughter.