iStock/Thinkstock(MOSCOW) — The Kremlin has denied that President Donald Trump’s national security adviser, Michael Flynn, discussed U.S. sanctions against Russia with Moscow’s ambassador to the U.S. ahead of Trump’s inauguration.

President Vladimir Putin’s spokesman, Dmitry Peskov, confirmed that phone calls between Flynn and Russia’s Washington ambassador, Sergey Kislyak, had taken place, but said reports that they had discussed sanctions were “wrong.”

On Thursday, The Washington Post reported that Flynn had explicitly discussed the sanctions with Kislyak during a series of phone calls in December based on interviews with current and former senior officials. The claims conflict repeated denials by Flynn and other senior members of the Trump administration that Flynn had broached the issue of sanctions during the calls.

Some of the U.S. officials, who headed government agencies at the time of the calls, told the Post they were concerned there may have been an inappropriate and potentially illegal attempt by Flynn to reassure the Kremlin on sanctions as the Obama administration was imposing measures against Russia in retaliation for allegedly interfering in the U.S. presidential election.

Flynn has denied the reports, saying initially the two had only exchanged Christmas greetings and discussed plans for a phone call between Trump and Putin. Last month, Sean Spicer, the White House press secretary, told reporters, “They exchanged logistical information on how to initiate and schedule that call. That was it. Plain and simple.” Spicer later told ABC News that Kislyak had called to invite the U.S. to talks on the Syrian conflict held in Kazakhstan recently.

ABC News has reached out to Flynn’s office for comment.

On Wednesday Flynn again denied he had discussed sanctions, but by Thursday the Post reported that a spokesman for Flynn “indicated that while [Flynn] had no recollection of discussing sanctions, he couldn’t be certain that the topic never came up.”

The questions over Flynn’s contacts with Kislyak were first raised in early January, when it emerged that he had spoken to the ambassador five times on Dec. 29, the same day that President Obama expelled 35 Russian diplomats from the U.S. and closed a handful of Russian diplomatic facilities as punishment for the alleged Kremlin meddling.

Concerns were raised by some administration officials that Flynn may have sought to undermine those sanctions in his call with Kislyak. After the expulsions, the Kremlin unusually declined a tit-for-tat response, instead inviting American diplomats in Moscow to a children’s Christmas party.

The Trump administration has backed Flynn’s story. In an interview last month, Vice President Mike Pence told CBS: “They did not discuss anything having to do with the United States’ decision to expel diplomats or impose censure against Russia.”

According to the Post, the FBI is examining Flynn’s communications with Kislyak. U.S. officials have said Flynn’s calls with Kislayk were picked up as part of routine surveillance of the Russian diplomat. According to the Post, further communications between Flynn and Kislyak were also conducted in person and by text message.

A senior administration official told ABC News last month that the White House has “absolutely no knowledge of any investigation or even a basis for such an investigation.”

Some of the officials in the Post story stressed the Obama administration was divided over how to interpret the calls. Several of the officials “emphasized that while sanctions were discussed, they did not see evidence that Flynn had an intent to convey an explicit promise to take action after the inauguration,” the Post said. The Logan Act, the law which Flynn is accused of potentially violating, forbids U.S. citizens from interfering in foreign policy.

The administration’s contacts with Russia are under scrutiny after U.S. intelligence concluded that the Kremlin had intervened in the elections to help Trump and harm his Democrat opponent, Hillary Clinton. A declassified report from the Director of National Intelligence in December found Russia had used cyberattacks and propaganda to try to undermine American democracy and to tilt the balance in favor of Trump. A broad Senate investigation is currently underway into the alleged interference; it is unclear whether the FBI’s investigation of Flynn is part of that.

Flynn’s attitude to Russia specifically has attracted criticism from some Democrats and Republicans, in particular a 2015 trip to Moscow to speak at an anniversary conference for the Russian propaganda network, Russia Today, where he dined at a table with Putin.

Publicly, including at the Moscow conference, Flynn has suggested he believes the U.S. should work with Russia to combat radical Islamic terrorism, which he has described as a “cancer.”

Congressional Democrats have written a letter to the Pentagon requesting more details on Flynn’s Moscow trip, seeking information on payments he received for speaking at the Russia Today conference.

“It is extremely concerning that General Flynn chose to accept payment for appearing at a gala hosted by the propaganda arm of the Russian government, which attacked the United States in an effort to undermine our election,” Rep. Elijah Cummings, the ranking Democrat on the House Committee on Oversight and Government Reform, wrote in the Feb. 1 letter.

Flynn has acknowledged that he was paid for speaking in Moscow, telling the Washington Post the invitation came through his speakers bureau.

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