Americans hoping to travel to North Korea will soon be required to obtain a special passport validation, the State Department announced Wednesday.

The validations will be "granted only under very limited circumstances" and will go into effect Sept. 1, according to a travel alert issued by the department.

The alert cites "serious and mounting risk of arrest and long-term detention of U.S. citizens under North Korea’s system of law enforcement" as the reason for rule.

The travel alert also directs all U.S. passport holders currently in North Korea to leave the country before the restrictions take effect.

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The Trump administration has taken steps to further restrict travel to North Korea after the death of U.S. college student Otto Warmbier on June 19.

Warmbier, 21, was imprisoned in the country for more than a year and a half before being returned to the U.S. in a coma. He died shortly afterward.

The State Department initially announced a ban on Americans traveling to North Korea last month.

The restrictions also come amid heightened tensions between Pyongyang and Washington, which has been incensed by the continued development of its missile and nuclear programs.

North Korea conducted its latest test of an intercontinental ballistic missile last week. The country's leader Kim Jong Un Kim Jong UnSatellite images indicate North Korea preparing for massive military parade South Korea warns of underwater missile test launch by North Korea Trump says he didn't share classified information following Woodward book MORE said the missile is capable of striking the mainland United States.