The only certain way to locate and secure all North Korea’s nuclear weapons sites would be via a US ground invasion, the Washington Post reported on Saturday, citing a letter from Pentagon officials sent to members of Congress.

It said the letter, reportedly written by the vice director of the Pentagon’s Joint Staff, noted that such a conflict could prompt Pyongyang to deploy biological and chemical weapons.

The report detailing the prospect of war on the Korean peninsula comes as President Donald Trump embarks on a nearly two-week Asia tour, with the North’s nuclear and missile program expected to top the agenda.

The US Defence Department sent the letter in response to a request from two members of Congress for details regarding "expected casualty assessments in a conflict with North Korea" for US and allied forces in Japan, South Korea and Guam as well as civilians, the Post said.

Tensions have soared over North Korea’s nuclear and missile programs in recent months, goaded by Trump and Pyongyang leader Kim Jong-un’s fiery exchanges of insults and warnings of conflict.