The Obama administration published a detailed assessment that laid the blame on the Kremlin

In 2017, the United States extracted from Russia an important CIA source who had provided information about the Kremlin's interference in the 2016 presidential election, according to current and former officials.

The operation, known as an exfiltration, followed mounting concerns among U.S. officials that the individual, whose identity is unknown, could be discovered by the Russian government.

The exfiltration took place sometime after an Oval Office meeting in May 2017, when President Donald Trump revealed highly classified counterterrorism information to the Russian foreign minister and ambassador, said the current and former officials, speaking on the condition of anonymity to discuss the sensitive operation.

That disclosure alarmed U.S. national security officials, but it was not the reason for the decision to remove the CIA asset, according to the current and former officials.

The exfiltration was first reported by CNN. The CIA declined to comment.

U.S. officials had been concerned that Russian sources could be at risk of exposure as early as fall 2016, when the Obama administration first confirmed that Russia had stolen and publicly disclosed emails from the Democratic National Committee and the account of Hillary Clinton's campaign chairman, John Podesta.

In October 2016, the Department of Homeland Security and the Office of the Director of National Intelligence said in a joint statement that intelligence agencies were "confident that the Russian Government directed" the hacking campaign.

"We believe . . . that only Russia's senior-most officials could have authorized these activities," the statement said.

Earlier drafts of the statement had accused Russian President Vladimir Putin by name, but the reference was removed out of concern that it could endanger sources and methods, The Washington Post reported.

In January 2017, the Obama administration published a detailed assessment that unambiguously laid the blame on the Kremlin, concluding that "Putin ordered an influence campaign" and that Russia's goal was to undermine faith in the U.S. democratic process and harm Clinton's chances at winning.

"That's a pretty remarkable intelligence community product - much more specific than what you normally see," one U.S. official said. "It's very expected that potential U.S. intelligence assets in Russia would be under a higher level of scrutiny by their own intelligence services."

"It's quite likely," the official continued, "that the U.S. intelligence community would already be taking a hard look at extracting any U.S. assets who would have been subject to increased levels of scrutiny" after the assessment's publication. Part of it relied on communications intercepts and human intelligence, the official said. The Russians "undoubtedly would have been conducting a review as to who within Putin's inner circle would have had access to the information." ​

Last year, Russian operatives traveled to England and used a nerve agent to try to kill a former Russian military intelligence officer, Sergei Skripal, who had become a British spy, according to U.S. and British officials. In 2006, Russian operatives killed former intelligence officer Alexander Litvinenko in London by placing radioactive material in his tea, according to a British investigation.

Current and former officials said an exfiltration is a methodical process not normally triggered by a single event. It takes time to arrange for the asset, and potentially family members, to be secretly removed from the country and resettled.

Serving as an asset or informant is dangerous work, and as the potential for exposure increases, "then it's not a surprise that these people are extracted," said one former senior U.S. official. "That's the good news story."

The current location of the Russian asset is not known.

