The United States issues ban on traveling to North Korea

American passports (AP file photo)

The United States has issued a ban prohibiting its citizens traveling to North Korea, following the death of an American national who was imprisoned in the Asian country over espionage charges.

The measure was introduced on Wednesday after American officials said the risk of arrest by North Korean officials presented an "imminent danger to the physical safety" of US citizens. The ban will come into effect on September 1.

 "All United States passports are declared invalid for travel to, in, or through the DPRK [Democratic People's Republic of Korea] unless specially validated for such travel," read the restriction in the US government's Federal Register.

Strict warnings against traveling to North Korea were already in place before the ban was first revealed last month following the death of university student Otto Frederick Warmbier who died after falling into a coma in a North Korean prison.

Warmbier, 22, spent 17 months in a North Korean jail over spying charges and was released to his family back in the US after falling into a coma due to a “severe neurological injury.” He died on June 19.

The casket carrying the remains of Otto Warmbier is carried out of  Wyoming High School in Wyoming, Ohio on June 22, 2017. (Photo by AFP)

North Korea has detained at least 17 American citizens over the past decade and three of them remain imprisoned there, according to official reports.

The US says it is concerned by the North Korea’s nuclear and missile tests. Pyongyang, in response, accuses Washington of plotting with regional allies to topple its government.

North Korea has so far conducted a total of five nuclear tests, in 2006, 2009, 2013 and twice in 2016, and numerous missile test-launches.

Pyongyang has defied sanctions and international pressure, saying it will continue to strengthen its military capability to protect itself from the threat posed by the presence of US forces in the region.

North Korea says it will not give up on its nuclear deterrence unless Washington ends its hostile policy toward Pyongyang and dissolves the US-led UN command in South Korea.