WASHINGTON (NYTIMES) - Secretary of State Mike Pompeo said he warned Russia against offering bounties for killing US and coalition troops in Afghanistan, even as President Donald Trump has denigrated as a "hoax" a CIA assessment that Russia carried out such a covert operation.

Mr Pompeo's remarks in an interview on Wednesday (Aug 12) came as new details emerged about one aspect of evidence, involving Russian passport numbers, that led CIA analysts to link the suspected bounty operation to the elite Unit 29155 of Russia's military intelligence agency, known as the GRU.

The Secretary of State also disclosed that the Pentagon similarly cautioned Russian military leaders about the suspected bounties as he acknowledged that he had delivered his own warning to Russia's Foreign Minister, Mr Sergey Lavrov.

"If the Russians are offering money to kill Americans or, for that matter, other Westerners as well, there will be an enormous price to pay. That's what I shared with Foreign Minister Lavrov," Mr Pompeo told Radio Free Europe and Radio Liberty during a trip to the Czech Republic, according to a State Department transcript.

"I know our military has talked to their senior leaders, as well. We won't brook that. We won't tolerate that."

By contrast, Mr Trump said late last month that he had not brought up the suspected operation when he spoke with President Vladimir Putin of Russia, dismissing it as "an issue that many people said was fake news".

Russian officials have denied the accusations.

Mr Pompeo provided few details about the warnings. He did not, for example, say whether it was a vague and abstract warning or whether he had threatened specific consequences.

He also did not specify who had delivered the Pentagon's message and to whom, or when.

However, a rare channel of direct, high-level communication between the two militaries involves General Mark Milley, the chairman of the Joint Chiefs of Staff, who spoke with his Russian counterpart, General Valery Gerasimov, six weeks ago, shortly after The New York Times first reported on the CIA assessment.

Asked whether Gen Milley raised bounties with Gen Gerasimov, Pentagon officials have responded by insisting that such conversations remain private so that the two men can maintain close contacts for use in times of strife.

Mr Pompeo also did not say when he had warned Mr Lavrov, but his remarks confirmed a New York Times report last week that he delivered such a message in a July 13 call, according to people briefed on the matter.

They said Pompeo had couched the warning as a hypothetical, even as he implied that he was referring to the reports about the CIA's assessment on Russian bounties in Afghanistan.

The New York Times first reported in June that the CIA had concluded that the Russian operatives had covertly offered and paid bounties to a Taleban-linked criminal network to incentivise more frequent attacks on US and other coalition troops in Afghanistan amid peace talks to end the long-running war there.

But even though the National Security Council assembled a range of potential responses, like a diplomatic warning or sanctions, months had passed and the White House authorised none of them.

Amid bipartisan criticism, the White House has defended its months of inaction by falsely suggesting that no one deemed the CIA assessment worthy of sharing with Mr Trump - in fact, it was in his written briefing in February, although officials have told Congress that his aides did not orally bring his attention to it - and by portraying the information as uncertain.

Amid the turbulence, details about its basis have trickled out.

The constellation of evidence included the accounts of interrogated Afghan detainees, a large seizure of cash found in a raid, data showing transfers of funds from a bank account controlled by the GRU to the Taleban, and travel records showing intermediaries going between Russia and Afghanistan.

There was an additional clue, two officials confirmed this week: At least one passport number used by someone suspected of involvement in the bounty operation was close to a narrow range of passport numbers that Western intelligence officials say are known to have been assigned to operatives from the GRU's Unit 29155, suggesting it came from the same batch.

The New York Times asked officials about passport numbers after an anonymously run blog called Nightingale, which focuses on Russian covert operations, reported on Tuesday that businessman Rahmatullah Azizi used a Russian passport number near that range.

US and Afghan officials have identified Mr Azizi as a key middleman believed to have handed out Russian money to Taleban-linked fighters for targeting coalition troops in Afghanistan. He is believed to be in Russia.

The officials confirmed that batch passport numbers were generally part of the intelligence that contributed to the CIA's assessment without discussing the blog's specific claims.

But the disclosure of the additional type of evidence further undercut the White House's portrayal of the intelligence as too insubstantial to merit presidential attention.

Unit 29155 has primarily been known for its links to several partly botched covert operations that came to light in Europe, including the 2018 nerve agent poisoning in Salisbury, England, of Mr Sergei Skripal, a former GRU officer who had worked for British intelligence and then defected, and his daughter; an attempted coup in Montenegro in 2016; and the poisoning of an arms manufacturer in Bulgaria a year earlier.

The US for years has accused Russia of sending arms and other support to the Taleban.

Offering bounties to encourage more killings of US and coalition troops would be a significant escalation.

Mr Pompeo was evasive when asked by Radio Free Europe whether his decision to deliver the warning to Mr Lavrov meant that he believed the assessment was credible, shifting the topic to reports about Russian and Iranian assistance to arm the Taleban.

"We've made clear we know the history; we know that the Russians have armed the Taleban in the past, right," he said.

"We know that the Iranians continue to arm them today. So we know these facts. We've made clear to each of them our expectations, and we will do everything we need to do to protect and defend every American soldier and, for that matter, every soldier from the Czech Republic or any other country that's part of the" mission in Afghanistan.