Jared Kushner, senior White House adviser and President Donald Trump’s son-in-law, was interviewed this month by Special Counsel Robert Mueller’s team as it investigates whether Trump associates colluded in Russia’s efforts to interfere in the 2016 U.S. election, said a person familiar with the matter.

The Mueller team’s questions to Mr. Kushner focused on the activities of former National Security Adviser Mike Flynn, the person said, as it probes Mr. Flynn’s ties to Turkey and Russia. The meeting—Mr. Kushner’s first known interview with the special counsel’s team—lasted less than an hour, the person said.

Abbe Lowell, a lawyer for Mr. Kushner, said in a statement, “Mr. Kushner has voluntarily cooperated with all relevant inquiries and will continue to do so.”

The Kushner interview marks the closest point Mr. Mueller has reached within the president’s orbit, said people familiar with the matter. The special counsel has already interviewed current and former top White House officials, including former chief of staff Reince Priebus, and is expected to interview others, including Communications Director Hope Hicks, in the coming weeks. The Kushner interview was first reported by CNN on Wednesday.

Mr. Trump has denied any collusion by him or his campaign, and Moscow has denied meddling in the election.