Donald Trump's son-in-law proposed a secret back channel between the Kremlin and the US president's transition team, it has been reported.
Jared Kushner, who was a top White House adviser, made the proposal at a meeting with the Russian ambassador to the US last December, a person familiar with the talks said.
The source said the aim was to connect Mr Trump's chief national security adviser at the time, Michael Flynn, with Russian military leaders.
Russia, a key player in Syria, has backed Syrian president Bashar Assad, often at the expense of civilians during a long civil war.
Mr Kushner's involvement in the plan was first reported by the Washington Post, which said he proposed using Russian diplomatic facilities for the discussions, apparently to make them more difficult to monitor.
The newspaper cited anonymous US officials who were briefed on intelligence reports on intercepted Russian communications.
Ambassador Sergey Kislyak was taken aback by the suggestion of allowing an American to use Russian communications gear at its embassy or consulate - a proposal which would have carried security risks for Moscow as well as the Trump team, said the Post.
The Trump team eventually felt there was no need for a back channel once Rex Tillerson was confirmed as secretary of state on February 1, said the source.
The team decided to communicate with Moscow through more official channels.
Mr Flynn served briefly as Mr Trump's national security adviser but was fired in February. Officials said he misled vice president Mike Pence about whether he and the ambassador had discussed US sanctions against Russia in a phone call.
This deception left Mr Flynn vulnerable to being blackmailed by the Russians, Sally Yates, the former acting attorney general, told Congress this month.
The FBI interviewed Mr Flynn, who remains under federal investigation in Virginia over his foreign business ties, in January about his contacts with Mr Kislyak.
The White House did not acknowledge the meeting with the Russian ambassador or Mr Kushner's attendance until March. A White House official dismissed it as a brief courtesy meeting at the time.
Mr Kushner's lawyers said he was willing to talk with federal and congressional investigators about his foreign contacts and his work on the Trump campaign.
National security adviser HR McMaster, speaking generally, said: "We have back channel communications with a number of countries. It allows you to communicate in a discreet manner."
Mr Kushner was a trusted Trump adviser last year, overseeing the campaign's digital strategy, and remains an influential confidant within the White House as does his wife, Ivanka Trump.
Reuters has reported that Mr Kushner had at least three previously undisclosed contacts with Mr Kislyak last year, including two phone calls between April and November.
But Mr Kushner's attorney Jamie Gorelick said his client "has no recollection of the calls as described."
Mr Trump immediately sought to dismiss recent news reports as "fake news."
"It is my opinion that many of the leaks coming out of the White House are fabricated lies," he tweeted.
He added: "Whenever you see the words 'sources say' in the fake news media, and they don't mention names ... it is very possible that those sources don't exist but are made up by fake news writers."
Investigators are also interested in a meeting Mr Kushner had with Russian banker Sergey Gorkov, according to reports.
Federal investigators and several congressional committees are looking into any connections between Russia and the Trump campaign, including allegations that there may have been collaboration to help Mr Trump and harm his Democratic opponent, Hillary Clinton.
The Senate Intelligence Committee, which is investigating Russia's meddling in the 2016 US presidential election, has requested information and documents from Mr Trump's campaign.
The request arrived last week at campaign headquarters in New York, according to a person familiar with the request.