President Donald Trump's son-in-law and senior adviser, Jared Kushner, denied in a statement Monday that he suggested setting up a "back channel" communication line to the Kremlin that would bypass US intelligence agencies and persist after Trump was inaugurated.

But Kushner acknowledged in the statement, which came ahead of a closed-door appearance before the Senate Intelligence Committee, that he asked Russia's ambassador to the US in December whether the Trump transition team could use Russia's embassy to communicate privately with Moscow about Syria.

The meeting with the ambassador, Sergey Kislyak, "occurred in Trump Tower, where we had our transition office, and lasted twenty [to] thirty minutes," Kushner wrote in an 11-page statement detailing his contacts with Russian nationals during the election and transition period.

"Lt. General Michael Flynn (Ret.), who became the President's National Security Advisor, also attended ... I stated our desire for a fresh start in relations."

Kushner said Kislyak, whose tenure in the US ended this past weekend, asked whether there was "a secure line in the transition office to conduct a conversation" about the US's Syria policy.

"General Flynn or I explained that there were no such lines," Kushner wrote. But he said he went on to ask whether the Russian Embassy "had an existing communications channel ... we could use where they would be comfortable transmitting the information they wanted to relay to General Flynn."

Kislyak said they didn't, according to Kushner, and "nothing else occurred."

"I did not suggest a 'secret back channel,'" he wrote. "I did not suggest an on-going secret form of communication for then or for when the administration took office. I did not raise the possibility of using the embassy or any other Russian facility for any purpose other than this one possible conversation in the transition period. We did not discuss sanctions."