Airlines continued to operate flights to Paris on Saturday, but the terror attacks in the French capital left tourists and business travelers wondering whether to cancel upcoming trips.

The attacks left the travel community on edge. Some would-be travelers quickly canceled trips to Paris, while the airlines let anxious customers with weekend tickets for Paris change plans without a fee.

Tensions were high at airports across Europe on Saturday.

A Paris-bound Air France jet was evacuated at Amsterdam's Schiphol Airport after authorities received a threatening tweet. At London's Gatwick Airport, a terminal was shut down for hours after a 41-year-old man from France was seen throwing away what looked like a gun. Authorities called in explosives experts.

U.S. authorities said that they had nothing to add to Friday night's comment by Homeland Security Secretary Jeh Johnson that officials didn't know of any specific or credible terror threats against the United States.

Air France said it would operate all upcoming flights to and from France but that delays were expected because of increased security measures at airports, including Paris' Charles de Gaulle Airport.

United Airlines and Delta Air Lines said that all their flights between the U.S. and Paris were operating, although Delta noted that many Paris departures were held up waiting for passengers to go through extra security screening. American Airlines said all its flights would run too, except a Paris-to-Dallas flight — that plane remained in Dallas when the Paris-bound leg was canceled Friday night.