WASHINGTON -- United Airlines on Tuesday extended its window for travelers wishing to change their South Korea-bound flights without paying a fee, as the number of coronavirus cases in the country continued to climb.

The US airline said on its website that passengers originally booked on flights departing from Feb. 24 to June 30 can switch to another flight within the same window, and between the same cities, without paying the change fee or any difference in fare.

On Monday the airline had said the waiver would apply to flights from Feb. 24 to April 30.

The revision comes after the US Centers for Disease Control and Prevention issued the highest type of travel health notice for South Korea, recommending that Americans avoid all nonessential travel to the country due to the spread of the coronavirus there.

As of Tuesday, there were 977 confirmed cases of the COVID-19 virus in South Korea, with 11 fatalities, including the death of a Mongolian national.

Travelers wishing to postpone their flight beyond June 30, or to change their departure or destination city, will be able to do so without paying the change fee but may still be required to pay any difference in fare, the airline added. The original ticket must have been purchased by Feb. 23.

Delta Air Lines took similar steps on Monday by applying a waiver to travel through April 30, with the rescheduled travel beginning no later than May 31.

United Airlines operates direct flights between San Francisco and Incheon. Delta flies to Incheon from Atlanta, Minneapolis and Detroit.

Other destinations currently on United's travel waiver list over the coronavirus include Wuhan, China, the epicenter of the outbreak; Beijing; Chengdu; Shanghai; and Hong Kong.

Delta only lists Beijing, Shanghai and Incheon.

On Saturday, the US State Department raised its travel advisory for South Korea by one notch to Level 2, urging travelers to exercise "increased caution." (Yonhap)