Washington DC - President Donald Trump's beleaguered national security adviser, Mike Waltz, reportedly made more than 20 group chats on Signal to discuss sensitive issues.

Politico spoke with four people who had personally been added to Signal chat groups by or with Mike Waltz, often to discuss sensitive national security-related topics and coordinate official work.

All in all, Waltz was reportedly in at least 20 chats, discussing issues including Ukraine, China, the Middle East, Africa, the European Union, and Gaza. All four sources confirmed that sensitive information about these topics was discussed.

"It was commonplace to stand up chats on any given national security topic," one source told Politico, before revealing that high-ranking Cabinet members were also often present.

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The report comes a little over a week since Waltz mistakenly added the editor-in-chief of The Atlantic to a Signal chat group discussing bombing of Yemen, in which dozens of civilians were killed. The former congressman has since also found himself in hot water over his use of Gmail for official work.

Speculation about Waltz being potentially fired has grown, but Trump has stood by him.

National Security Council (NSC) spokesperson Brian Hughes tried to justify the use of Signal by claiming that it is "an approved, encrypted messaging app."

In a statement to the Daily Beast, however, he insisted that "Any claim of NSC officials sending classified information over these channels is false."

"It can be used for unclassified messaging and a user has the responsibility to preserve any official record created."