In a statement Tuesday, the Dutch Military Intelligence and Security Service said it had discovered malware installed in a computer network being used by its military, blaming a Chinese state actor.

In response, China's embassy in The Hague insisted Beijing "always firmly opposes and cracks down on cyber attacks in all forms in accordance with the law".

"We will not allow any country or individual using Chinese infrastructure to engage in such illegal activities," it said in a statement on its website.

"China opposes any malicious speculations and groundless accusations," it added, describing cyber security as a "common challenge of all countries".

Dutch intelligence said the malware had exploited a known vulnerability in systems provided by Fortinet, a cybersecurity firm.

It was found on a network engaged in non-classified R&D, it added.

The United States has warned that China represents "the broadest, most active, and persistent cyber espionage threat" to its government and private sector.

Last month, Washington said it had dismantled a China-based hacking network known as "Volt Typhoon", accusing it of infiltrating critical US infrastructure networks with the goal of disabling them in the event of conflict.

Beijing has dismissed the claims as "groundless" -- and pointed to the United States' own history of cyber espionage.