US cyber weapons are being developed. Reuters Pictures The US government live-tested its digital weapons arsenal during a three week series of war games, leading to fresh concerns it is preparing for “cyber war.”

According to The Wall Street Journal the war games involved the Pentagon, Department of Homeland Security (DHS), National Security Agency NSA and an undisclosed number of unnamed “UK officials” and “private companies.”

At the time of publishing, none of the mentioned US departments or the UK Cabinet Office had responded to Business Insider’s request for comment.

The exercises were reportedly held at the US Suffolk, Va military base in June. The tests saw participants split into 14 teams and tasked to mitigate simulated attacks.

The final stage of the games saw the participating private companies ejected from the event so the military teams could test cyber “response actions,” which is a codeword for counterattacks.

The US is one of many countries believed to be developing cyber weapons. The US has constantly accused China of developing and using cyber weapons against it.

Democratic presidential candidate Hillary Clinton accused China of trying to "hack into everything that doesn't move in America," during a speech on Saturday. And digital activist group Greatfire.org reported the Chinese government had developed a cyber weapon, called “Great Cannon,” in April.

The US military’s cyber offensive capabilities have been the source of ongoing international debate and the nature of the counterattack strategies and tools used during games remain unknown. The country is believed to have played a role developing several cyber weapons, including the Stuxnet malware.

Stuxnet is sabotage-focused malware that was originally caught targeting Iranian nuclear facilities in 2011. The malware is viewed as a game changer as it attempted to physically break the power plant, not shut down its IT systems.

Reuters reported the US tried to mount a Stuxnet-style computer virus campaign against North Korea but failed in May.

The June war games had a focus on critical infrastructure attacks, like Stuxnet and simulated strikes on oil and gas pipelines, “a major commercial port in the UK,” Pentagon networks, banks and food suppliers.