US launches multi-agency search to find source of huge Ukraine document leak

The United States has launched a multi-agency investigation after highly classified military and intelligence documents containing sensitive information on topics including Ukraine’s defence were leaked online.

The documents included information about a range of topics relating to the war in Ukraine, China, the Middle East, and Africa, with many officials suspecting that they may have been leaked by an American, rather than an ally.

"The focus now is on this being a US leak, as many of the documents were only in US hands," Michael Mulroy, a former senior Pentagon official told Reuters.

The investigation is in its early stages, and officials have not ruled out the possibility that pro-Russian elements could be behind the leak.

Some Western security experts and US officials have expressed suspicion that the leak, which started anonymously from Discord and 4Chan and was reported by the New York Times last week, could be the work of someone from within the United States.

Over 50 documents labelled “secret” and “top secret” that appeared on social media in the last few weeks were reviewed by the Reuters news agency, which reported that some documents also appeared altered.

Two US officials told Reuters that they have not ruled out that the documents may have been doctored to mislead investigators as to their origin or to disseminate false information that may harm US security interests.

The agency said the authenticity of the documents in circulation could not be verified independently but reported that one document giving battlefield casualty estimates from Ukraine appeared to have reportedly minimized Russian losses.

A document marked "secret" outlined in detail how Ukraine's S-300 air defence systems would be depleted by 2 May at the current usage rate. The information could potentially be of great use to Russian forces, and Ukraine said its president and top security officials met on Friday to discuss ways to prevent leaks.

Another document marked "top secret" said the Mossad intelligence agency was encouraging protests against Israeli prime minister Benjamin Netanyahu's plans to tighten controls on the Supreme Court.

In a statement on Sunday, Mr Netanyahu’s office described the assertion as “mendacious and without any foundation whatsoever.”

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

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

The Pentagon has not addressed the leaks in particular but said in a statement on Sunday, that it was reviewing the validity of the photographed documents that “appear to contain sensitive and highly classified material.”

The White House has referred questions to the Pentagon, which referred the issue to the Department of Justice, which has opened a criminal investigation.

The leak is seen as one of the most serious security breaches since more than 700,000 documents, videos, and diplomatic cables appeared on the WikiLeaks website in 2013.

Officials told Reuters on condition of anonymity that they are investigating possible motivations for the leak, including a disgruntled employee or an insider threat who actively wanted to undermine US national security interests.

Additional reporting by agencies