Washington DC - A new trove of documents purportedly containing US military secrets about Ukraine, China, and the Middle East has surfaced online, according to reports.

More than 100 classified documents, which were published on Twitter and elsewhere on Friday, contained information on the status of the fighting in the eastern Ukrainian city of Bakhmut, for example, the New York Times reported.

The documents appear to have originated from the US military and intelligence services, and were also posted on the chat app Discord, the Wall Street Journal said.

The Defense Department is investigating the posts, spokespersons told both outlets.

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The Times cited an anonymous senior official as calling the leak "a nightmare for the Five Eyes," referring to the intelligence sharing partnership among the United States, Britain, Australia, New Zealand, and Canada.

In addition to information on Ukraine, the batch of documents also contained classified "briefing slides" on China, the military situation in the Indo-Pacific, the Middle East, and terrorism.

This is the second time in days that Washington and its allies have been blindsided by such disclosures.

On Thursday, the Times reported war documents pertaining to Ukraine's preparations for a looming spring counter-offensive and the status of its air defense capabilities had been posted on social media channels.

The source of the documents remains unclear, and it is not known how much more classified information has leaked out, the reports said.