US National Security Advisor Mike Waltz received emails via his personal email account but has never used that account to send classified material, the White House has said.
It comes after The Washington Post reported Mr Waltz and other National Security Council members used Gmail for government work.
The Post said yesterday that Mr Waltz and other NSC members used the Alphabet-owned commercial email service to conduct government business.
That report came a week after the Trump administration's security practices came under bipartisan criticism following its use of the Signal messaging app to coordinate military action in Yemen.
One aide of Mr Waltz used Gmail to share information involving sensitive military positions and powerful weapon systems tied to an unspecified ongoing conflict, it reported, citing documents it reviewed and interviews with three US officials.
Mr Waltz had less sensitive, but still exploitable, information sent to his personal email, including his schedule and other work documents, the Post reported.
NSC Spokesman Brian Hughes, asked about the report, said: "NSA Waltz received emails and calendar invites from legacy contacts on his personal email."
"He has never sent classified material over his personal email account or any unsecured platform," Mr Hughes said yesterday.
Mr Waltz copied in government email accounts for items received after US President Donald Trump took office on 20 January to comply with federal records laws, he added.
Mr Hughes said all NSC staff are informed that "classified material must only be sent through secure channels" and that "any non-government correspondence must be captured and retained for record compliance."
Mr Waltz, US Defense Secretary Pete Hegseth and others have faced sharp criticism following revelations last month that they used Signal - an encrypted commercial messaging app where messages expire - to coordinate and share highly sensitive details about a planned military operation targeting the Houthis in Yemen, rather than using secure government communications channels.
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Critics have said the move was a breach of US national security and could be a violation of law.
The administration officials' discussions were shared when a reporter for The Atlantic magazine was inadvertently added to the Signal chat.
Members of Mr Trump's administration, including Mr Waltz and Mr Hegseth, have in the past levelled harsh criticism at former Democratic presidential candidate Hillary Clinton for her use of a private email server when she was secretary of state during the Obama administration.
On Monday, the White House said Mr Trump maintained confidence in Mr Waltz and considers the Signal case closed.
Spokesperson Karoline Leavitt declined to give details about the administration's review of the Signal incident but told reporters steps were taken to ensure it would not happen again.
Republican and Democratic senators have called for a formal probe.
US House Democratic Leader Hakeem Jeffries slammed Mr Waltz following the latest revelations involving Gmail.
"Mike Waltz is totally and completely unqualified to be in a sensitive national security position, as is the case with the Trump national security team," Mr Jeffries told Axios in an interview yesterday.
