White House officials were first informed in early 2019 of intelligence reports that Russia was offering bounties to Taliban-linked militants to kill U.S. and coalition military personnel in Afghanistan, but the information was deemed sketchy and in need of additional confirmation, according to people familiar with the matter.

Several discussions were held with members of the National Security Council staff on the reports, which had been flagged as potentially significant and came at a time of growing tensions between Russia and the United States. Instructions were given to the intelligence community and the U.S. Central Command, one person familiar with the briefings said, to “find out more” about the bounty reports before proposing any action be taken.

Intelligence provided by captured Afghan militants suggested the bounty operation was in existence as far back as 2018, according to three people familiar with the matter, who like others spoke on the condition of anonymity because of the subject’s sensitivity.

Senior members of President Trump’s national security team indicated that they were not aware of the early intelligence, suggesting that it was mainly reviewed by lower-level officials.

It was unclear whether John Bolton, the White House national security adviser at the time, relayed information about that initial intelligence directly to Trump. Asked about it via an aide, Bolton said he had no comment.

Later, Bolton wrote on Twitter: “If reports that Russia offered bounty payments to Taliban forces for killing Americans in Afghanistan are true, it’s tantamount to an attack on Americans directly. At a minimum, we must consider strong economic sanctions as part of a comprehensive response.”

The White House’s awareness of the intelligence in 2019 was first reported by the Associated Press.

Intelligence analysts believe that the bounties probably resulted in the deaths of three Marines killed in April 2019 when the vehicle they were traveling in was blown up just outside Bagram, the main U.S. air base in Afghanistan, according to four people familiar with the matter.

This week, White House officials have said that intelligence about the Russian bounty program — which was examined again by the NSC in March — was not sufficiently substantiated to be brought to Trump’s attention.

At a White House briefing Tuesday, press secretary Kayleigh McEnany did not deny media reports on the intelligence, but repeated administration insistence that the information has not yet been “verified,” a process she said had been hindered by news leaks. The leaks, she said, were “targeted . . . against this president” and had damaged “our ability as a nation to collect intelligence.”

While numerous intelligence and former government officials have said that such reports would normally have reached the highest levels of government, including the president, McEnany said Trump is briefed only “when there is a strategic decision to be made.”

Trump, she said, has now been “briefed on what is unfortunately in the public domain,” although that “does not change the fact that there is still no consensus” within the intelligence community on its veracity.

But several people familiar with the matter noted that information is sometimes withheld from Trump, who often reacts badly to reports that he thinks might undermine what he considers his good relationship with Russian President Vladimir Putin.

The White House was “not the kind of environment, as in almost any business office, where you look to confront your boss with something,” Bolton said in a Washington Post interview last week. “And those are the circumstances we all worked in.”

It is not known whether the subject of the bounty reports came up last year in regular conversations between Gen. Joseph F. Dunford Jr., then chairman of the Joint Chiefs of Staff, and his Russian counterpart, Gen. Valery Gerasimov. That was the customary channel for the United States to raise concerns with Russia on military matters.

In the early White House discussion of the reports, officials questioned the reliability of the sources of the information, aware that both the Taliban and the Russians were known to spread disinformation. More-recent information about the Russian bounty program has also come from captured militants in Afghanistan, current and former officials said.

Late on Tuesday, Defense Secretary Mark T. Esper said the Pentagon would do everything in its power to keep American troops safe. “Although the Department of Defense has no corroborating evidence at this time to validate the recent allegations regarding malign activity by Russian personnel against US forces in Afghanistan, I want to assure all of our service members that the Department takes very seriously any and all potential threats against U.S. military personnel,” he said in a statement.

Russia’s military intelligence agency, the GRU, which U.S. officials say ran the bounty program, was known to have been given a relatively free hand to engage in operations to rattle the Americans, according to several people familiar with administration assessments.

At the same time, the Russians were believed to want revenge for a number of perceived American transgressions, particularly against Russian interests in Syria. Among them were U.S. air and artillery strikes in February 2018 on forces in Syria that included members of the Wagner Group, a mercenary force run by a Russian businessman close to Putin that includes former members of Russian military and intelligence units. The U.S. strikes killed hundreds of attackers.

As U.S. officials last year weighed the closely held information about Russia paying bounties, disagreements about its credibility and importance were set aside until more information was available, people familiar with the matter said. The extent to which more intelligence made its way to the White House before the end of 2019 is uncertain.

But in February of this year, after discoveries of questionable militant cash flows and the interrogation of prisoners in Afghanistan, information again made its way to the NSC. In late March, after a restricted, high-level meeting at the White House, the CIA was tasked with assessing it.

CIA analysts determined that the information was credible and showed a Russian plot to target U.S. and coalition forces, current and former officials familiar with the matter said. One former official said that there was a significant amount of intelligence and that it left little doubt among those examining it that Russia was targeting American forces.

The National Security Agency, which examines intercepted communications, took a more skeptical view of the 2020 information and the credibility of the underlying sources, people familiar with the information said. But some said the disagreements between the NSA and the CIA have been overstated by Trump administration officials.

Potentially important intelligence is traditionally shared with the president and senior officials before it has been fully vetted, assessed and subjected to the scrutiny of several intelligence agencies, a former official said.

The 2020 information was deemed credible and significant enough to be included this spring in the President’s Daily Brief, which is produced for the president and shared with top aides. In May, it was converted for broader distribution in The Wire, a regular CIA compendium of intelligence reports, which may be accessed by other agencies as well as certain congressional officials, people familiar with the matter said.

“The President’s Daily Brief traditionally includes the best assessments that analysts can provide on the issues of the most importance to the president,” said David Priess, a former CIA briefer and author of “The President’s Book of Secrets,” about the secretive PDB and how it is constructed.

“The primary criterion for putting an assessment into the PDB is not whether it has universal analytic agreement, but whether it will help the president address threats to national security or take advantage of opportunities in foreign policy,” Priess said.

House Democrats sharply criticized administration officials for not doing more to make sure Trump was aware of the Russian operation, even if the intelligence community had not fully verified the information.

“There are frequently times that the president of the United States will be briefed along with caveats . . . but you don’t deprive the president of information he needs to keep the troops safe because you don’t have it signed, sealed and delivered,” House Intelligence Committee Chairman Adam B. Schiff (D-Calif.) said after a briefing at the White House on the matter. “If you’re going to be on the phone with Vladimir Putin, this is something you ought to know.”

Some Republicans countered that the information, as they understood it, didn’t merit Trump’s attention. Sen. Ron Johnson (Wis.), who received a briefing on the intelligence from senior White House officials Monday, called it “unverified and completely not actionable.”

“This is not a big deal,” Johnson said. “The president’s got a big job, he can’t be made aware of every piece of unverified intelligence, and that’s what this was: unverified intelligence.”

Democrats said Tuesday that Washington should start considering sanctions on Russia for targeting U.S. troops, while leading House Republicans called for even harsher potential retaliatory measures.

“America’s adversaries should know, they should have no doubt, that any targeting of U.S. forces by Russia, by anyone else, should face a very swift and deadly response,” Rep. Liz Cheney (R-Wyo.) told reporters.

Secretary of State Mike Pompeo, who spoke Monday with the chief Taliban negotiator about ongoing U.S.-Taliban peace talks, said on Twitter that he pressed the militants “to live up to . . . their commitments . . . including, not to attack Americans.”

John Hudson, Greg Miller and Missy Ryan contributed to this report.