The United States has lowered its travel warning for South Korea by a notch to Level Two on its four-tiered system, which advises its citizens to exercise "increased caution."

The U.S. State Department on Tuesday announced the revised advisory on its homepage, saying it was lowered by one notch as of Monday.

As for the reasons, the department said that South Korea has resumed most transportation options, including airport operations, and business operations including day cares and schools. It added that other improved conditions have been reported. 

The U.S. placed a "Reconsider Travel" advisory, the second-highest warning, on South Korea in August.