the 2018 poisoning of a former G.R.U. officer, Sergei V. Skripal, in Salisbury, England, and of “assassinations across Europe.”

Unit 29155 was involved in two explosions at ammunition depots that killed two Czechs in 2014. He said the government would expel nearly 80 Russian diplomats.

Days later, the prosecutor general’s office in Bulgaria announced that it was investigating a possible connection between Unit 29155 and four explosions at ammunition depots over the past decade. At least two happened while members of the unit were frequently traveling in and out of Bulgaria, the office said.

Some of the destroyed arms in both countries, according to officials, belonged to Emilian Gebrev, a Bulgarian arms manufacturer who was poisoned in 2015 along with his son and an executive in his company. Officials have previously accused Unit 29155 in that attempted assassination.

While most previous reports about Unit 29155’s activities have centered in Europe, its leader, Maj. Gen. Andrei V. Averyanov, has experience in Central Asia. He graduated in 1988 from the Tashkent Military Academy in what was then the Soviet republic of Uzbekistan, a year before the Soviet pullout from bordering Afghanistan.

The government apparently did not declassify everything. The White House statement described but did not detail certain evidence, keeping its sources and methods of information-gathering secret. It did not specify the G.R.U. unit’s number, but officials have said it was Unit 29155, and the two prior operations the statement mentioned have been attributed to it elsewhere.

as a middleman for the Russian spies, and Habib Muradi. Both escaped capture and are said to have fled to Russia.

And it made no mention of other circumstantial evidence officials have previously described, like the discovery that money was transferred from a G.R.U. account to the Afghan network.

In an interview published April 30 in a Russian newspaper, Nikolai Patrushev, the chairman of Russia’s Security Council, again said it was false that Russia had covertly offered bounties for killing American troops in Afghanistan, adding that there was no evidence that it had done so.

The White House statement also brought into sharper focus two gaps in the available evidence that analysts saw as a reason to be cautious.

Military leaders have repeatedly pointed to one in public: The intelligence community lacks proof tying any specific attack to a bounty payment. “We cannot confirm that the operation resulted in any attacks on U.S. or coalition forces,” the National Security Council said.

The other reason for caution is an absence of information showing that a Kremlin leader authorized Unit 29155 to offer bounties to Afghan militants. “We do not have evidence that the Kremlin directed this operation,” the statement said.

The Biden administration’s briefing to reporters last month reignited a debate over the political implications of the C.I.A.’s assessment — and the Trump White House’s handling of it — that unfolded last year and dwelled in part on confidence levels.

reported last June on the existence of the C.I.A. assessment and that the White House had led an interagency effort to come up with options to respond but then authorized none.

Facing bipartisan criticism, the Trump administration defended its inaction by playing down the assessment as too weak to take seriously, falsely denying that it had been briefed to President Donald J. Trump. In fact, it had been included in his written presidential daily briefing in late February, two officials have said.

In congressional testimony, military leaders based in the United States who regularly interacted with the Trump White House said they would be outraged if it were true, but they had not seen proof that any attack resulted from bounties. But some military officials based in Afghanistan, as well as some other senior Pentagon and State Department officials, thought the C.I.A. was right, according to officials familiar with internal deliberations at the time.

Among those who found the evidence and analysis persuasive was Nathan Sales, the State Department’s politically appointed top counterterrorism official during the Trump administration.

“The reporting that Russia was placing bounties on American soldiers’ heads was so serious that it warranted a robust diplomatic response,” Mr. Sales said this week in an email.

A top Pentagon official and the secretary of state at the time, Mike Pompeo, later delivered warnings over the issue to their Russian counterparts, effectively breaking with the White House.

After the briefing last month, some Trump supporters — as well as some left-wing critics of the C.I.A. and military interventions — argued that the C.I.A.’s bounty assessment had been debunked as evidence-free “fake news,” vindicating Mr. Trump’s dismissal of the issue last year as a “hoax.” Russian propaganda outlets echoed and amplified those assertions.

Michael J. Morell, a former acting director of the C.I.A., said another factor had fostered confusion. When analysts assess something with low confidence, he said, that does not mean they think the conclusion is wrong. Rather, they are expressing greater concerns about the sourcing limitations, while still judging that the assessment is the best explanation of the available facts.

“A judgment at any confidence level is a judgment that the analysts believe to be true,” he said. “Even when you have a judgment that is low confidence, the analysts believe that judgment is correct. So in this case, the analysts believe that the Russians were offering bounties.”

Charlie Savage and Eric Schmitt reported from Washington, and Michael Schwirtz from New York. Julian E. Barnes contributed reporting from Washington.

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