(Reuters) - The United States is tightening controls on China’s imports of civil nuclear technology to prevent use for military or other unauthorized purposes, the U.S. Department of Energy said on Thursday amid increased trade tensions.

A cut-away model of the Chinese Gen-III nuclear power technology HPR1000 by China General Nuclear Power Corporation (CGN) is displayed at the World Nuclear Exhibition (WNE), the trade fair event for the global nuclear community in Villepinte near Paris, France, June 26, 2018. REUTERS/Benoit Tessier

Last month, U.S. President Donald Trump imposed tariffs on nearly $200 billion of Chinese imports and then threatened more levies if China retaliated. China then hit back with tariffs on about $60 billion of U.S. imports.

Washington announced the nuclear technology controls a day after the U.S. Justice Department said it had arrested and indicted a spy for China’s Ministry of State Security on charges of economic espionage. Chinese operative Xu Yanjun also attempted to steal trade secrets from U.S. aviation and aerospace companies, the department said. China rejected the allegations.

“The United States cannot ignore the national security implications of China’s efforts to obtain nuclear technology outside of established processes of U.S.-China civil nuclear cooperation,” U.S. Secretary of Energy Rick Perry said in a statement.

Beginning last year, the National Security Council led a review of China’s efforts to obtain nuclear material, equipment and advanced technology from U.S. companies, government officials said in a conference call with reporters on Thursday. The review was prompted by China’s accelerated efforts to acquire U.S. intellectual property to the detriment of U.S. businesses and military interests, they said.

The officials said the indictment in 2016 of a Chinese-American nuclear engineer, Allen Ho, was one of the factors that led to the review.

Ho, a naturalized U.S. citizen, pleaded guilty last year to conspiring to produce “special nuclear material” in China in violation of the U.S. Atomic Energy Act. The state-owned China General Nuclear Power Company (CGNPC) was also charged.

The new policy goes into immediate effect, and sets guidelines for reviewing all existing and future technology transfers into China, the officials said. The vast majority of existing technology transfers approved before Jan. 1, 2018 are unlikely to be altered, the officials said.

There will be a presumption of denial to new license applications or extensions to existing authorizations related to the CGNPC, the energy department said. Officials declined to comment on whether China is already using this technology.

The development of nuclear technology to power small reactors in the South China Sea and for submarines and icebreakers are of concern, officials said. They also expressed concern about use of the technology in weapons.

The government is also concerned about diversion for use of technology by other countries, one of the officials said. They declined to comment on the specifics of these concerns.

U.S. nuclear exports to China amounted to $170 million in 2017, the officials said.