The US State Department late on Wednesday confirmed that it would ban US citizens from travelling to North Korea from 1st September, and said that those already there should leave before the deadline.

Those wishing to travel to the reclusive state would have to obtain a special passport validation which would only be granted in very limited circumstances, the State Department said.

According to Deutsche Presse-Agentur, DPA, the announcement comes days after North Korea test-fired its second intercontinental ballistic missile and said that all the US mainland was now within its range. It is believed to be working on a nuclear missile capable of reaching the US.

In June, a US student who had been jailed in North Korea for allegedly trying to steal a propaganda banner from his hotel was returned to the US in a coma and died days later.

Otto Warmbier, a University of Virginia student, had been on a tour of North Korea when he was arrested and later sentenced to 15 years in a labour camp after a one-hour trial in March 2016.

Three other Americans are currently being held by Pyongyang, added DPA.

Wednesday's step was authorised by Secretary of State Rex Tillerson due to the serious and mounting risk of arrest and long-term detention of US citizens under North Korea's system of law enforcement, the State Department said.