The U.S. Department of Justice on Saturday said it has opened an investigation into the leaks of several classified U.S. military documents that were posted on social media in recent days.

The leaked classified documents touch not only on U.S. support for Ukraine but also highly sensitive analyses of U.S. allies like Israel and South Korea.

"We have been in communication with the Department of Defense related to this matter and have begun an investigation. We decline further comment," a spokesperson for the Department of Justice said in a statement.

The Pentagon on Thursday said it was looking into the matter, and a spokesperson for the Central Intelligence Agency on Saturday said the agency was "aware of the social media posts and are looking into the claims."

What do the documents say?

According to the New York Times and the Washington Post, the first tranche of documents appeared to have been posted in early March on Discord, a social media chat platform popular with video gamers.

On Wednesday, images showing some of the documents began circulating on the anonymous online message board 4chan and made their way to at least two mainstream social media platforms, Telegram and Twitter.

Information in the documents is at least five weeks old, with the most recent dated March 1.

The documents included precise details about the Ukrainian battlefield, use of U.S. weapons by Ukraine and the training of Ukrainian troops.

A new batch of classified documents leaked on Friday also detailed U.S. national security secrets from Ukraine to the Middle East to Asia.

CNN reported the topics of these leaked documents ranged from the Wagner Group's operations in Africa and Israel's pathways to providing lethal aid to Ukraine, to intelligence about the United Arab Emirates' ties to Russia and South Korean concerns about providing ammunition to the U.S. for use in Ukraine.

Iran's nuclear program and the Democratic People's Republic of Korea's missile program are also mentioned.

CNN cited an anonymous U.S. official who said these documents "look real."

As of Saturday, photographs of the documents were still being posted on various social media platforms.

What are the consequences of the leaks?

Mick Mulroy, a former senior Pentagon official, told the New York Times that the leak of the classified documents represents "a significant breach in security" that could hinder Ukrainian military planning.

"As many of these were pictures of documents, it appears that it was a deliberate leak done by someone that wished to damage the Ukraine, U.S. and NATO efforts," said Mulroy.

According to the New York Times, one of the U.S. intelligence officials described the leak as "a nightmare for the Five Eyes," in a reference to the United States, Britain, Australia, New Zealand and Canada, the so-called Five Eyes nations that broadly share intelligence.

The Washington Post reported that officials in several countries said that they were trying to assess the damage from the disclosures, and many were left wondering how they had gone unnoticed for so long.

(With input from agencies)

(Cover: Pentagon is seen from an airplane over Washington D.C., the U.S., February 19, 2020. /Xinhua)