The Senate Intelligence Committee said President Trump's adviser and son-in-law Jared Kushner failed to disclose that he had used a private email address to conduct official White House business.

On Thursday, committee Chairman Richard Burr, R-N.C., and Vice Chairman Mark Warner, D-Va., sent a letter to Kushner and his lawyer, Abbe Lowell, saying they were "concerned" to learn about the email address from news reports instead of Kushner himself.

Kushner appeared before the committee in July in a closed session, as part of the committee's probe in Russian meddling in the 2016 presidential election and possible collusion with Trump associates.

"As you are aware, this committee has previously requested that you preserve and produce certain documents related to the Russian inquiry—including, but not limited to, email communications," says the letter, first reported by CNN.

The senators sent their letter just days after Lowell confirmed to news organizations that Kushner used a private email address to conduct some official White House business. According to Lowell, the email was created during the transition and had fewer than 100 email exchanges from January through August.

The committee requested that Kushner confirm that the documents he provided to the committee included the additional personal email account referenced by Lowell.

They also asked for any other email accounts, messaging apps or similar forms of communications channels Kushner may have used "relevant to our inquiry."