WASHINGTON — Jared Kushner, President Trump’s son-in-law and senior adviser, spoke in December with Russia’s ambassador to the United States about establishing a secret communications channel between the Trump transition team and Moscow to discuss strategy in Syria and other policy issues, according to three people with knowledge of the discussion.

The conversation between Mr. Kushner and the ambassador, Sergey I. Kislyak, took place during a meeting at Trump Tower that Mr. Trump’s presidential transition team did not acknowledge at the time. Also present at the meeting was Michael T. Flynn, the retired general who would become Mr. Trump’s short-lived national security adviser, the three people said.

It is unclear who first proposed the communications channel, but the people familiar with the meeting said the idea was to have Mr. Flynn speak directly with a senior military official in Moscow to discuss Syria and other security issues. The communications channel was never set up, the people said.

The three people were not authorized to discuss the December meeting and spoke on the condition of anonymity. The White House declined to comment on Friday night.