Chinese state-sponsored hackers breached Singapore Telecommunications, the largest mobile carrier in Singapore, during the summer, according to a recent report citing 2 people familiar with the matter.

The breach was discovered in June, but news about it only came to light today. Investigators believe that the responsible party for the attack is a group called Volt Typhoon. Volt Typhoon has gained access to critical infrastructure sectors in the United States, such as telecommunications and energy.

According to the 2 people who spoke to Bloomberg, the cyber breach at Singtel, which operates extensively in Southeast Asia and Australia, was an exercise by China aimed at future intrusions into U.S. telecommunications networks.

Despite this, China contends that its cybersecurity agencies have released evidence suggesting that Volt Typhoon is actually being used by an international ransomware organization.

“China firmly opposes and combats cyber attacks and cyber theft in all forms,” Liu Pengyu, a spokesperson for the Chinese Embassy in Washington, said, adding that he wasn’t familiar with the details of the incident.

When reached for a comment, SingTel responded, but didn’t directly address the breach.

“We understand the importance of network resilience, especially because we are a key infrastructure service provider. That’s why we adopt industry best practices and work with industry-leading security partners to continuously monitor and promptly address the threats that we face on a daily basis. We also regularly review and enhance our cybersecurity capabilities and defenses to protect our critical assets from evolving threats,” the company said.

In a separate statement, a SingTel spokesperson confirmed “[t]here was a malware detected in June, which was subsequently dealt with and reported to relevant authorities. There was no data exfiltrated and no impact to services.”

However, the spokesperson refused to say whether this incident was the same one being referenced, adding, “We do not comment on speculation.”