Story highlights The State Department announced the travel ban last month

Three Americans are currently in North Korean captivity

(CNN) The Trump administration's ban on US citizens traveling to North Korea will take effect early next month, and include exemptions for journalists and humanitarian workers.

The proposed policy posted to the Federal Register on Wednesday, a State Department official tells CNN, and takes effect on September 1.

The administration will continue to permit four categories of travelers to visit North Korea after the policy takes effect, by applying for a special validation to their passport. Those categories are journalists, Red Cross officials, applicants whose travel is "justified by compelling humanitarian considerations," and individuals whose visit is "otherwise in the national interest."

In a travel alert released Wednesday, the State Department urged all Americans currently in North Korea to leave the country before the policy takes effect next month.

The State Department announced the travel ban last month amid mounting concern over the safety of US citizens visiting the secretive and geopolitically isolated country.

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