Chinese hackers breached the US government office that reviews foreign investments for national security risks, three US officials familiar with the matter told CNN.

The theft, which has not previously been reported, underscores Beijing’s keen interest in spying on a US government office that has broad powers to block Chinese investment in the US as tensions between the world’s two superpowers remain high.

The breach was part of a broader incursion by the hackers into the Treasury Department’s unclassified system. The office targeted by the hackers, the Committee on Foreign Investment in the US (CFIUS), in December gained greater authority to scrutinize real estate sales near US military bases. US lawmakers and national security officials have grown increasingly worried that the Chinese government or its proxies could use land acquisitions to spy on those bases.