The US national security community is grappling with fallout from the release of dozens of secret documents, including the impact on sensitive information-sharing within the government and ties with other countries, two US officials said.

Reuters has reviewed more than 50 of these documents, labelled “Secret” and “Top Secret”, that first appeared on social media websites in early March and purportedly reveal details of Ukrainian military vulnerabilities and information about allies including Israel, South Korea and Turkey. The material did not draw much notice until a New York Times article on Friday.

Reuters has not independently verified the documents’ authenticity. US officials have said some giving battlefield casualty estimates from Ukraine appeared to have been altered to understate Russian losses.

The leak was sufficiently alarming within the Pentagon that it referred the matter to the Department of Justice, which has opened a criminal investigation into the disclosure of the documents.

Two US defense officials, speaking on condition of anonymity because of the sensitivity of the matter, said the Pentagon was examining procedures governing how widely some of the most sensitive US secrets are shared.

Some of the documents, one of the officials said, would most likely have been available to thousands of people with US and allied government security clearances despite being highly sensitive, as the information directly affected those countries.

The Pentagon on Sunday said in a statement that an interagency effort was assessing the impact the photographed documents could have on US national security as well as that of close American allies, a standard procedure known as “damage assessment” for leaks of classified information.

The first official said the number of people who had access to the documents underscores that sensitive information was perhaps being shared too widely with personnel who might not require the level of detail some of the documents contained.

“The Pentagon has needed to curtail the unbridled access to some of the most sensitive intel when they’ve (got) no justifiable reason to have it,” the first official said.

The two officials said further that although the leaks were highly concerning, many of them provided only snapshots of time in February and March - when they were dated - but did not appear to disclose anything about future operations.

Although the release of documents appears to be the most serious public leak of classified information in years, officials say it so far does not reach the scale and scope of the 700,000 documents, videos and diplomatic cables that appeared on the WikiLeaks website in 2013.

SEARCHING FOR A MOTIVE

The first defense official said Pentagon investigators were trying to determine who would have an incentive to leak this kind of information.

Since the leak first came to light in March, the investigators have been pursuing theories ranging from someone simply sharing the documents to show off the work they were doing to a mole inside the US intelligence community or military, the first official added.

Daniel Hoffman, a former senior CIA undercover officer, said that given past activities of Moscow’s intelligence agencies, it was “highly likely” that Russian operatives posted documents related to Ukraine as part of a Russian disinformation operation.

He said such operations - meant to sow confusion, if not discord, among Russia’s adversaries - were a “classic” practice of Russian spy services to leak authentic documents in which they have inserted false information.

The aim, he said, appeared to be to drive a wedge between Ukraine and the United States, Kyiv’s largest provider of military support.

Some national security experts and US officials say they currently suspect that the leaker could be American, given the breadth of topics covered by the documents, but they do not rule out pro-Russian actors. More theories could develop as the investigation progresses, they said.

The Kremlin and the Russian embassy did not respond to a request for comment about whether it was involved in the leak.

Ukraine said its president and top security officials met on Friday to discuss ways to prevent leaks.

The White House has declined to discuss publicly who might be responsible for the breach and has referred all questions about the leak to the Pentagon. The Pentagon said that over the weekend, US officials spoke with allies and notified the relevant congressional committee about the leak.

“I’m deeply troubled by the possible extent and nature of the information exposed and expect to be fully briefed in the days to come,” said Representative Jason Crow, a former Army Ranger who sits on the US House of Representatives intelligence and foreign relations committees.

IMPACT ON ALLIES

The leaks have already drawn responses from some foreign governments.

In a statement on Sunday, Israeli Prime Minister Benjamin Netanyahu’s office labeled as “mendacious and without any foundation whatsoever” a document asserting that the Mossad, one of the country’s intelligence agencies, encouraged recent protests against Netanyahu’s plan to tighten controls on the judiciary.

A South Korean presidential official said on Sunday the country was aware of reports about the leaked documents and planned to discuss “issues raised” with Washington.

One of the documents gave details of internal discussions among senior South Korean officials about US pressure on Seoul to supply weapons to Ukraine, and its policy of not doing so.

One of the documents marked “Top Secret” purportedly detailed how Russian private military contractors met with Turkish “contacts” to buy weapons from Ankara.

The Turkish embassy in Washington declined to comment.

Some of the most sensitive information is purportedly related to Ukraine’s military capabilities and shortcomings.

It is not uncommon for the United States and other countries to spy on their allies. But public disclosures of such spying are uncomfortable for those allies, who need to explain to their populations how they will respond.

“It is going to take some time to rebuild trust with our allies,” the second US defense official interviewed by Reuters said.

Michael Mulroy, a former senior Pentagon official, played down the lasting impact of the leak.

“It is of course embarrassing when these activities become publicly disclosed,” Mulroy said. “It may cause short-term problems for the relationships but I believe long-term the shared interests between the countries will still be strong.”