Chinese hackers recently infiltrated the US Treasury Department’s Office of Foreign Asset Control (OFAC) in a significant incident reported by the Washington Post on Wednesday.

The Treasury Department informed US lawmakers about the cyberattack in a letter dated December 30, attributing the breach to a state-sponsored Advanced Persistent Threat (APT) actor from China. The incident occurred on December 8, although the department did not specify which offices were affected or the nature of the stolen files, only indicating that “certain unclassified documents” were compromised in this major event.

As reported by the Washington Post, the hackers focused on OFAC and the office of Treasury Secretary Janet Yellen. Anonymous US officials suggested that the attackers were likely seeking information regarding Chinese entities that the US might sanction.

President Joe Biden has imposed sanctions on numerous Chinese companies for allegedly providing ‘dual use’ goods—items that can serve both military and civilian purposes—to the Russian military. Both Biden and former President Donald Trump have also targeted Chinese telecommunications firms over suspected espionage activities and have enacted export controls on specific equipment utilized by Chinese semiconductor manufacturers.

Mao Ning, the spokesperson for the Chinese Foreign Ministry, stated on Tuesday that Beijing does not regard “such baseless accusations that lack evidence” with any seriousness.

“China has consistently opposed all types of hacking activities and is particularly against the dissemination of false information aimed at discrediting China for political gain,” Mao remarked.

The purported cyberattack was reported less than a month after U.S. authorities accused a hacking group allegedly linked to Beijing, known as ‘Salt Typhoon,’ of infiltrating the systems of nine American telecom companies. It is claimed that the hackers monitored the communications of Trump and his campaign team, as well as collected surveillance data that the companies had gathered for U.S. law enforcement agencies.

The Chinese embassy in Washington, D.C. has refuted these allegations.