North Korea is conducting biological weapons experiments to test the possibility of loading anthrax-laden warheads on its intercontinental ballistic missiles, it has been reported.

Japan's Asahi newspaper reported on Wednesday, citing an unidentified person connected to South Korean intelligence, that North Korea was conducting biological weapons experiments to test the possibility of loading anthrax-laden warheads on its intercontinental ballistic missiles.

The Asahi report said the U.S. government was aware of the tests, which were meant to ascertain whether the anthrax bacteria could survive the high temperatures that occur during warheads re-entry from space.

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Pyongyang has tested a missile that could hit the eastern seaboard of the United States 

The news that North Korea may have been testing anthrax-laden warheads comes as  South Korean President Moon Jae-in is seeking to soothe relations with China and the North before the Winter Olympics in South Korea in February.

He suggested on Tuesday he was prepared to postpone military drills with the United States.

Pyongyang sees the joint exercises as preparation for war, while Beijing is still angry about the deployment of a U.S. anti-missile system, commonly known as THAAD, by South Korea.

China believes the system's powerful radar can see far into its territory, but Seoul argues it needs it to guard against the threat posed by North Korea's missile and nuclear programmes.