(CNN) A cybersecurity firm says hackers were able to infiltrate a European Union communications system for years and copy thousands of sensitive diplomatic cables, The New York Times has reported.

Area 1, the cybersecurity firm which discovered the vulnerability, said thousands of EU diplomatic cables were accessed using "techniques resembling those long used by an elite unit of China's People's Liberation Army," according to the Times.

The EU's secretariat told the Times it was "aware of allegations regarding a potential leak of sensitive information and is actively investigating the issue."

If confirmed, such a hack would represent a stunning breach of security in what appears to be an audacious act of espionage.

In a statement to CNN, China's Ministry of Foreign Affairs said reports like the one published by the Times are "suspicious, groundless" and "extremely irresponsible."

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