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

China denied the claims, 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".

"We have stated our position many times regarding such groundless accusations that lack evidence," Foreign Ministry spokeswoman Mao Ning said.

According to the US Treasury, the incident happened earlier this month, when the actor compromised a third-party cybersecurity service provider and was able to remotely access the workstations and some unclassified documents.

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 ascertain 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.

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

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