USA: After yet another significant leak, a large number of classified US national security files have surfaced online, according to the New York Times, which also notes that the new documents contain "sensitive" information regarding terrorism, China, the Middle East, and the Ukraine.

One day after other "top secret" documents revealing US and NATO war plans in Ukraine circulated on social media, there was another breach.

In what one senior US intelligence official called a "nightmare" for Western security services, the new cache of documents was discovered on Twitter and other platforms on Friday afternoon, according to the NYT.

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The outlet speculated that the most recent breach may have "more than 100 documents" in total, though the full extent of the leak has not yet been determined and the authenticity of the files has not been confirmed.

Some of the files contain information on intelligence related to the conflict in Ukraine, similar to another classified disclosure that was first reported on Thursday. After months of ferocious fighting, Moscow has largely taken control of the city of Artyomovsk (also known as Bakhmut in Ukraine), according to one "top secret" document.

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The NYT continued, stating that the scope of the breach appears to have caught the White House "off guard," adding that the new leak does not stop with Ukraine and covers a variety of other topics, including "sensitive briefing slides on China, the Indo-Pacific military theatre, the Middle East, and terrorism."

The Justice Department later announced its own separate investigation after the Pentagon announced on Thursday that it would look into the matter. It claimed to be in contact with military authorities, but neither party provided any further information.

Officials promised to take down the information from the internet after the earlier leak this week, but many of the documents are still available on social media, suggesting that they have not been successful.

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Finding the source of the breach would start with "identifying which officials had access to them," according to one unnamed official quoted by the NYT. Many national security agencies' employees spoke of a "rush" to identify the leaker and expressed worry that this week's revelations would turn into a "steady drip of classified information" posted online.