Beijing, China - China on Tuesday hit back at accusations that a state-sponsored actor was behind a cyber breach at the US Treasury Department, calling the claims "groundless."

The Treasury said the attack resulted in access to some of its workstations, according to a letter to Congress seen by AFP.

It claims the incident happened earlier this month, when the attacker compromised a third-party cybersecurity service provider and was able to remotely access the workstations and some unclassified documents.

China denied claims it was involved, with the foreign ministry saying Beijing "has always opposed all forms of hacker attacks, and we are even more opposed to the spread of false information against China for political purposes."

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"We have stated our position many times regarding such groundless accusations that lack evidence," foreign ministry spokesperson Mao Ning said.

The Treasury contacted the US Cybersecurity and Infrastructure Security Agency after it was alerted of the situation by its provider BeyondTrust, and has been working with law enforcement to evaluate the impact.

"The compromised BeyondTrust service has been taken offline and there is no evidence indicating the threat actor has continued access to Treasury systems or information," the department's spokesperson said.

In its letter to the leadership of the Senate Banking Committee, the Treasury wrote: "Based on available indicators, the incident has been attributed to a China state-sponsored Advanced Persistent Threat (APT) actor."

An APT refers to a cyberattack where an intruder establishes and maintains unauthorized access to a target, remaining undetected for a sustained period of time.

The department did not provide details on what was affected by the breach or evidence for its claims, but said more information would be released in a supplemental report at a later date.

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"Treasury takes very seriously all threats against our systems, and the data it holds," the spokesperson added.

Several countries, notably the US, have for years claimed that Chinese-government-backed hacking activity is targeting their governments, militaries, and businesses.

Beijing rejects the allegations, and has previously said that it opposes and cracks down on all forms of cyberattacks.