The U.S. government's suspicion of China's use of its supercomputers for "nuclear explosive activities" is keeping Intel from selling its Xeon Phi chips to the country.

The Santa Clara, Calif.-based company's chips are used by China's TianHe-1A and TianHe-2, two of the fastest supercomputers in the world, according to CNN Money. Supercomputers can simulate weather, nuclear explosions and other types of environments in order to predict different scenarios that could happen in the future.

News sources only discovered this week that the U.S. Department of Commerce established a new federal rule in February that requires all American companies to apply for a special permit in order to export any product to four Chinese supercomputing centers, one of which is at the National University of Defense Technology in Changsha City.

The U.S. government said these supercomputing centers were "acting contrary to the national security... interests of the United States," adding that "the TianHe-1A and TianHe-2 supercomputers are believed to be used in nuclear explosive activities."

The TianHe-2 uses 80,000 Xeon chips to produce over 33 petaflops of computational capacity, which is one of the reasons why the supercomputer has held the title of the world's most powerful computing machine for the past 18 months, Gizmodo reported. One petaflop equals about one quadrillion calculations per second.

China is estimated to have 250 nuclear warheads, while the U.S. has 1,642 and Russia has 1,643, CNN Money reported.

The U.S. government has yet to offer an explanation for why it believes China would use Intel's chips for nuclear activities. While Intel hasn't commented on the situation, a company spokesman said the company is abiding by U.S. laws.