"Once in effect, U.S. passports will be invalid for travel to, through and in North Korea, and individuals will be required to obtain a passport with a special validation in order to travel to or within North Korea," Nauert said.

The move was due to "mounting concerns over the serious risk of arrest and long-term detention under North Korea's system of law enforcement," she added.

North Korea has detained two Korean-American academics and a missionary, a Canadian pastor and three South Korean nationals who were doing missionary work there. Japan says at least several dozen of its nationals are being held in the country.