(CNN) House Oversight Chairman Elijah Cummings said Thursday his committee has obtained new information that several senior White House officials have used personal email and messaging accounts to conduct government business, asserting that President Donald Trump's son-in-law communicated with foreign leaders through a private messaging application that appears to lack adequate safeguards.

In a Thursday letter to the White House, the Maryland Democrat alleged that Jared Kushner, who is also a senior White House adviser, had been using WhatsApp, a popular messaging application, to "communicate with foreign leaders" -- something he said that Kushner's attorney had confirmed in a private meeting. He also contended that Trump's daughter Ivanka Trump, also a senior adviser, may be in violation of the Presidential Records Act by her use of private emails.

The allegations from Democrats that some of Trump's closest confidants -- as well as former officials Steve Bannon and K.T. McFarland -- used personal email come as Trump continues to attack Hillary Clinton for using a private email system when serving as secretary of state.

In the letter, Cummings revealed that his panel learned the new information in a private meeting in December with Abbe Lowell, an attorney for both Kushner and Ivanka Trump. Lowell referred inquiries to the White House and National Security Council about whether Kushner communicated classified information through WhatsApp, something that Cummings said would constitute a "major security breach."

"For example during a meeting with Mr. Kushner's attorney, Abbe Lowell, Mr. Lowell confirmed that Mr. Kushner has been using the messaging application WhatsApp as part of his official White House duties to communicate with foreign leaders. Mr. Lowell could not answer whether Mr. Kushner's communications included classified information," Cummings wrote.

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