The Justice Department has joined the Pentagon in an urgent effort to determine how secret military documents on the war in Ukraine made their way onto multiple social media sites.

A small number of documents, including some marked "top secret," were found on Twitter and Telegram on Wednesday. Since then, journalists, researchers, and social media sleuths have uncovered additional classified documents posted as early as March 1 on additional sites. This raises a host of questions about how widespread the breach may be and how much damage it could cause.

Pentagon officials acknowledge the documents are real and say they are investigating. The Department of Justice said Friday evening it has also opened an investigation and is working with the Department of Defense.

There's no word on who might be responsible for leaking or stealing the documents.

Also, the motive for putting the material online is unclear, since government intelligence agencies around the world seek to conceal, rather than reveal, secret documents they obtain.

Some of those posting the documents on social media appear to be individuals hiding behind an alias, and they seem to be reposting versions they came across elsewhere. So far, the original source for posting the documents online has not been publicly identified.

Mikhailo Podolyak, a senior advisor to Ukraine's President Volodymyr Zelenskyy, said on Twitter that he believed Russia was responsible. He called it an attempt to "divert attention, cast doubts and mutual suspicions, sow discord."

Documents on several social media platforms

NPR has viewed documents on a number of sites, including Twitter, Telegram, Discord and 4chan.

In addition to Ukraine, some of the documents provide assessments of China and countries in the Middle East.

Many include maps of Ukraine and charts on where troops are concentrated and what kinds of weapons are available to them. The online posts show photos of physical documents that were folded and creased in some instances.

Some are dated to late February or early March and appear to be part of a slide deck produced daily for top U.S. military and other national security officials.

One document is labeled "Top Secret," and is titled "Status of the Conflict as of 1 March." It gives a detailed battlefield summary from Ukraine on that day.

Military analysts say they believe the original versions of the documents were slightly altered in some instances.

For example, one chart puts the Ukrainian death toll at around 71,000, a figure considered plausible. However, the chart also lists the Russian fatalities at 16,000 to 17,500. The Russian count is believed to be much larger, though neither side releases overall casualty figures.

How valuable to Russia?

The public disclosure of classified material on the Ukraine war is both alarming and embarrassing for the U.S., and Russia is sure to scrutinize the documents.

However, assessing the value to Russia is difficult to determine, especially at this early stage, when the full extent of the breach is not known.

The papers published online do not reveal Ukrainian battle plans for a widely expected offensive this spring.

A senior Ukrainian security official, Oleksii Danilov said that no more than five people know when and where the Ukrainian operation will begin.

However, the online documents do mention combat brigades that Ukraine is assembling and when they should be ready to fight. There's also information on the rate at which Ukraine is burning through ammunition. While this issue has been discussed publicly by the U.S. and Ukraine, the documents provide details that have not been disclosed.

Before the war, Russian intelligence agencies were considered extremely active in Ukraine. Russia and Ukraine were both part of the Soviet Union, and Russian President Vladimir Putin, a former intelligence agent himself, has meddled in Ukrainian affairs throughout his time in power, including an initial 2014 military incursion.

In the runup to Russia's full-scale invasion in February 2022, the U.S. intelligence community intentionally publicized some information about Russian military plans.

The goal was to persuade the international community that the threat of a Russian attack was real. CIA Director William Burns has made multiple visits to Ukraine and spoken about the ongoing intelligence sharing between the two countries.

Prior to the war, some U.S. officials expressed concerns that Russian intelligence could gain access to the information the U.S. was providing to Ukraine. But the intelligence sharing among the U.S., NATO and Ukraine has been seen as extremely valuable in helping the smaller Ukrainian military fight off the Russians.

On the battlefield, the Russians continue to press a months-long offensive in eastern Ukraine, in and around the town of Bakhmut, but the Russian military has only made progress in heavy fighting that has claimed thousands of casualties on both sides.

The Ukrainians are widely expected to launch their own offensive soon, and most analysts expect it to focus on areas controlled by Russian troops in southeastern Ukraine.