The incident happened earlier this month, when the actor compromised a third-party cyber security service provider and was able to remotely access the treasury workstations and some unclassified documents, a treasury spokesman added.

Treasury contacted the cyber security and infrastructure security agency after it was alerted of the situation by its provider BeyondTrust, and has been working with law enforcement partners 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 spokesman added.

In its letter to the leadership of the senate banking committee, the treasury said: “Based on available indicators, the incident has been attributed to a China state-sponsored advanced persistent threat (APT) actor.”

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.