REPUBLIKA.CO.ID, WASHINGTON -- A ban on travel by U.S. passport holders to North Korea will take effect on Sept. 1 and Americans in the country should leave before that date, the U.S. State Department said on Wednesday.

Journalists and humanitarian workers may apply for exceptions to the ban, the department said in a public notice.

The U.S. government last month said it would bar Americans from traveling to North Korea due to the risk of "long-term detention" there.

The ban comes at a time of heightened tensions between the United States and North Korea, which has been working to develop a nuclear-tipped missile capable of hitting the United States.