Due to the Novel Coronavirus (Covid_19) the US State Department issued a level 4 travel advisory stating, in part, that “Citizens who live abroad should avoid all international travel. If you choose to travel abroad your travel plans may be abruptly interrupted and you may be trapped outside of the United States indefinitely.”
The State Department has also warned US citizens traveling abroad to return home immediately. For those citizens that are stranded, the State Department is looking for solutions that will bring them home, including using military planes as an option.
A level 4 travel advisory is the highest level the State Department can issue. It is usually reserved to restrict travel to countries with war zones or high probability of terrorist activity, etc.