News - Middle East: Confidential documents detailing the US and the NATO military alliance plans to militarily assist Ukraine in launching a spring offensive against Russia have surfaced online, prompting a Pentagon probe.

The documents marked "top secret" – reportedly containing charts and details on weapons deliveries, battalion strengths and other sensitive material -- were leaked on Twitter and Telegram social media platforms, the New York Times reported on Thursday, citing Defense Department officials.

"We are aware of the reports of social media posts, and the Department is reviewing the matter," Deputy Press Secretary Sabrina Singh said in the report, suggesting that an investigation into the security breach is underway.

According to the US-based daily, one of the documents summarized the training schedules of 12 Ukraine combat brigades and added that nine of them were being trained by US and NATO forces, further pointing out that 250 tanks and more than 350 mechanized vehicles were needed for the effort.

The report stated that information in the documents also details expenditure rates for munitions under Ukraine military control, including for the HIMARS rocket systems, the US-made artillery weapon widely publicized in Western media reports as being highly effective against Russian forces.

It further noted that the documents -- at least one of which carried a "top secret" label -- were circulated on pro-Russian government channels.

The report quoted military analysts as claiming that some of the documents appear to have been altered in a “disinformation campaign” by Russia, claiming that in one document deaths of Ukrainian troopers were inflated while Russian battlefield losses were minimized.

The daily also cited officials as saying that the information in the documents is at least five weeks old, with the most recent dated March 1.

The development came amid persisting US-led efforts to send more weapons to Ukraine to further escalate the military campaign against Russia.