The Washington Post quoted U.S. officials as saying that the Pentagon's top command restricted the flow of information last Friday, in response to the leak of classified documents about the Ukraine war.
The Pentagon's restriction of the flow of information is extraordinarily strict and reveals a high level of panic among the leadership.
A European intelligence official told the newspaper that Europe was concerned that Washington could restrict allies' access to future intelligence reports.
In the same context, the Wall Street Journal quoted US officials as saying that the Pentagon is focused on finding out how dozens of highly classified documents were leaked, and that the White House is concerned about the repercussions of the leak.
The Pentagon is currently studying a range of possibilities for how the breach occurred, including that someone with top-secret security clearance leaked the information or that U.S. intelligence systems were compromised, the officials said.
According to the officials quoted by the newspaper, the unauthorized disclosure of highly sensitive information worries not only senior U.S. security officials, but also allies with whom classified intelligence is shared, as the leaked documents include intelligence on countries including Israel, Britain and South Korea.
Impact on America's Security
The officials the Wall Street Journal spoke with said the leak likely had an impact on U.S. national security around the world, adding that although the leaked documents are two months old, they could affect the course of the war in Ukraine, especially as the leaks expose potential weaknesses in the battle and the structure of Ukrainian forces.
Separately, an official at South Korea's presidential palace said on Sunday that Seoul was aware of media reports about the leak of several classified U.S. military documents and that it planned to discuss the issues raised by the leaks.
The New York Times reported on Sunday that the leaked documents contained details of private discussions among senior South Korean officials about U.S. pressure on the Asian ally to help supply Ukraine with weapons and Seoul's policy of not doing so.
Seoul has agreed to sell artillery shells to help the United States replenish its weapons stockpile, insisting that the "end user" must be the U.S. military. But senior South Korean officials were concerned that the United States would supply them to Ukraine.
The classified report was based on intelligence signals, meaning the United States was spying on one of its key allies in Asia.
The South Korean presidential official declined to answer reporters' questions about U.S. spying on the country or confirm any details contained in the leaked documents.
Asked if South Korea planned to lodge a protest or demand an explanation from the United States, the official, who asked not to be named, said the government would review previous cases and cases involving other countries.