Why It Matters: Support for Ukraine could be at risk.

While some U.S. officials are becoming more comfortable with Ukraine’s covert attacks on Russia, concerns remain about the possibility of miscalculation by Ukraine while conducting such operations. Sabotaging the Nord Stream pipelines was exactly the kind of operation that would concern the United States — a symbolic attack with little military value that carries a high risk of fracturing the alliance supporting Ukraine.

So far, that has not happened. Even as Germany and other European countries have learned of Ukrainian involvement in the pipeline attack, they have nevertheless increased their military aid.

American officials insisted on Tuesday there has been no determination about who within the Ukrainian government may have planned or authorized the attack. If it is eventually pinned on senior officials, European attitudes about support for Ukraine could change.

Background: Ukraine’s control over covert action groups is murky.

The Post withheld some details of the intelligence, including the name of the European country giving the report to the United States, to protect the sources of the information.

U.S. officials have long acknowledged they were aware of a warning that came from a European ally about a potential attack on the pipelines, but for months after the attack they maintained they were unsure who conducted it.

While officials acknowledged there was some early intelligence pointing to Ukraine, they said it was contradicted by other material, in essence saying they did not believe the European warning was a smoking gun.

As the investigation continued, U.S. and allied officials became more convinced that pro-Ukrainian groups carried out the attack and parts of the Ukrainian government were somehow involved.

The Post reported that the European intelligence report said the Ukrainian operatives involved in the plot to destroy the pipelines reported to Gen. Valeriy Zaluzhnyi, Ukraine’s senior military officer.

American officials have still not confirmed General Zaluzhnyi’s involvement. But they said again on Tuesday that they do not believe President Volodymyr Zelensky knew about it. Officials have previously described a system created by Ukraine’s government that insulates Mr. Zelensky from covert action programs.

That allows parts of the Ukrainian government to use pro-Ukrainian groups or sympathizers in Russia to conduct covert attacks, and for Mr. Zelensky to deny responsibility for such actions.

What’s Next: Europe is still investigating.

The C.I.A. declined to discuss the document or the attack investigation. John F. Kirby, a spokesman for the National Security Council, said he would not discuss intelligence matters, highlighting that the document was “one that The Washington Post even said was not corroborated by U.S. intelligence agencies.”

Mr. Kirby said the United States was still awaiting the results of three ongoing investigations of the Nord Stream sabotage.

Officials say the United States is unlikely to place any public blame for the destruction of the pipelines on Ukraine until after those investigations are done.

Aishvarya Kavi contributed reporting.