LONDON, April 11 (Xinhua) -- A leak of classified U.S. Defence Department documents is a "very serious" risk to national security of the United States, the British Broadcasting Corporation (BBC) said on Tuesday, citing the Pentagon.

Highly classified Pentagon documents were leaked online in recent weeks. The documents appear to include sensitive information regarding the war in Ukraine, as well as on China and U.S. allies, it said.

Other documents reportedly focus on "defense and security issues in the Middle East as well as in the Indo-Pacific region", it added.

The documents were "a very serious risk to national security and have the potential to spread disinformation," BBC reported, citing a high-ranking Pentagon official.