The United States imposed sanctions on Monday on Chinese hackers and accused them of working as a front for Beijing’s top spy agency, part of a broad effort to place malware in American electric grids, water systems and other critical infrastructure.

The sanctions were a major escalation of what has become an increasingly heated contest between the Biden administration and Beijing.

While there have been no cases so far in which the Chinese government has turned off essential services, American intelligence agencies have warned in recent months that the malware appeared to be intended for use if the United States were coming to the aid of Taiwan.

By turning off critical services to military bases, and to civilian populations, China would attempt, according to a series of intelligence findings, to turn Americans inward — worrying about their own supplies of electricity, food and water rather than coming to the aid of a distant island that Beijing claims as its own.

The sanctions were part of a joint effort between the United States and the United Kingdom to crack down on Chinese hacking into vital services. In announcing the new measures, the Treasury Department described malicious state-sponsored cyberactors as “one of the greatest and most persistent threats to U.S. national security.”

The Treasury Department added Wuhan Xiaoruizhi Science and Technology Company to its sanctions list and described it as a “front company” for China’s ministry of state security. The ministry has emerged as Beijing’s largest hacking operation, after a major investment by the Chinese government, according to American intelligence agencies.