TOKYO (BLOOMBERG) - North Korea has begun tests to load anthrax onto intercontinental ballistic missiles, Japan's Asahi newspaper reported on Tuesday (Dec 19), citing an unidentified person connected to South Korea's intelligence services.

The report said the testing involves ensuring the anthrax survives the immense temperatures generated during re-entry into the Earth's atmosphere.

North Korea has a stockpile of between 2,500 tonnes to 5,000 tonnes of chemical weapons, and is capable of producing biological agents such as anthrax and smallpox, South Korea has previously said.

The Asahi report comes a day after the White House published its National Security Strategy, a document that said Pyongyang is "pursuing chemical and biological weapons which could also be delivered by missile".

"North Korea - a country that starves its own people - has spent hundreds of millions of dollars on nuclear, chemical, and biological weapons that could threaten our homeland," the report said.

North Korea claimed it had completed its nuclear force after it fired a new Hwasong-15 ICBM in late November.

South Korea assessed the missile - North Korea's largest yet - could potentially fly 13,000 kilometres and reach Washington, though additional analysis was needed to determine whether it was capable of re-entry.