The German airline Lufthansa resumed daily direct flights to Cairo on Sunday after a one-day suspension due to unspecified safety concerns.

But British Airways still has all its flights to the Egyptian capital grounded and plans to keep them that way for six more days.

The two airlines on Saturday abruptly canceled all flights to Cairo after the British government warned of a "heightened risk of terrorism against aviation."

Egypt's minister of civil aviation, Lt. General Younes Elmasry, on Sunday expressed frustration that the airline suspended flights without consulting Egyptian authorities. He met with Britain's Ambassador to Egypt Geoffrey Adams and said the two sides would work to resolve the situation as soon as possible.

Passengers scrambled to find alternative flights after receiving a notification from the airline informing them about the decision which came into effect immediately.

In a statement, British Airways said the move was "a precaution to allow for further assessment", without offering further details.

The U.S. State Department warned citizens Friday about traveling to Egypt. "A number of terrorist groups, including Islamic State, have committed multiple deadly attacks in Egypt, targeting government officials and security forces, public venues, tourist sites, civil aviation and other modes of public transportation, and a diplomatic facility," the State Department said. "Terrorists continue to threaten Egypt's religious minorities and have attacked sites and people associated with the Egyptian Coptic Church."

It also warned of "risks to civil aviation operating within or in the vicinity of Egypt."

No American flights have been affected so far.