WASHINGTON (Reuters) - The U.S. energy secretary on Thursday signed an order prohibiting electric utilities that supply critical defense facilities from importing certain power system items from China, in an effort to protect U.S. security from cyber and other attacks. The Department of Energy said in a release the order prohibits utilities that supply the defense facilities at a service voltage of 69kV or above from acquiring, importing, transferring, or installing bulk power system electric equipment. It was not immediately clear which defense sites were considered critical and the Energy Department did not immediately respond to a request for comment. Bulk power equipment consists of items used in substations, control rooms, or power plants, including nuclear reactors, capacitors, transformers, large generators and backup generators and other equipment. “It is imperative we secure the (bulk power system) against attacks and exploitation by foreign adversaries,” Energy Secretary Dan Brouillette said in the release. Brouillette said it is one of the steps the Trump administration is taking to “diminish the ability of our foreign adversaries to target our critical electric infrastructure.” The ban takes effect on Jan. 16, days before the inauguration of President-elect Joe Biden. It follows President Donald Trump’s signing of a related executive order in May that had been expected to put barriers on some power grid imports from China and Russia. It also came days after it was revealed that hackers believed to be working for Russia breached the U.S. Treasury and Department of Commerce and other agencies. In 2018, the Trump administration blamed the Russian government for a campaign of cyber attacks over at least two years that targeted the power grid including nuclear power and manufacturing facilities. It was the first time Washington publicly accused Moscow of hacking into American energy infrastructure.