The New York Times, citing online posts reviewed by the newspaper, reported that the U.S. Air National Guard operative accused of leaking classified documents to a small chat group was posting sensitive information months earlier than previously known and to a much larger group.

The newspaper said on Friday that in February 2022, shortly after the outbreak of the war in Ukraine, an account on the social networking platform Discord comparable to that of Jack Teixeira, a member of the US National Guard, began publishing classified intelligence about the Russian war effort on a previously undisclosed chat group.

The newspaper said the group had about 600 members. She added that the chat room in question was publicly listed on a YouTube channel for the videos and was easily accessible.

The Pentagon declined to comment on the new information reported by the New York Times.

Last week, a 21-year-old U.S. Air National Guard operative, who faces criminal charges for leaking top-secret military intelligence documents online, was arrested.

Teixeira's relatives leave court after appearing before her (Reuters)

The New York Times said the newly discovered information posted on the larger chat group included details of dead and wounded Russian and Ukrainian troops, the activities of Moscow's intelligence agencies and updates on aid to Ukraine.

The user claimed to be disseminating information from the National Security Agency, the CIA and other intelligence agencies, she said.

The case is believed to be the most serious U.S. security breach since more than 700,2010 documents, videos and diplomatic cables appeared on WikiLeaks in <>. The Pentagon called the leak a "deliberate criminal act."

The leaks were not highlighted until the New York Times published them in early April, although the documents had been published earlier than that date.

Teixeira faces a charge of violating the Espionage Act relating to the copying and transmission of sensitive defence material, as well as a charge of illegally transporting defence material to an unauthorized location. Legal experts said he was likely to face further charges.