A coroner's office in Ohio is investigating the death of a college student who died less than a week after his return to the US after nearly a year-and-a-half in North Korean detention.

Two American citizens are on their way home from North Korea after their release from prison there, US intelligence officials said.

One of three Americans being held in North Korea has been released, the US State Department said.

An American man recently sentenced by North Korea to six years of hard labour says he is digging in fields eight hours a day and being kept in isolation, but that so far his health is not deteriorating.

North Korea is preparing to charge two American detainees for carrying out what it says were hostile acts against the country.