German airline Lufthansa canceled about 800 flights Monday, affecting some 10,000 passengers worldwide, after more than 4,000 pilots began a four-day walkout over job security. Europe's biggest airline by sales said many long-haul flights to the U.S., including New York and Denver, were canceled because of the strike organized by the Cockpit pilots' union. However, it said it was still running many domestic flights and short-haul routes across Europe, the Associated Press reported. Other flights to the U.S., including Newark, New Jersey, Dallas and Chicago were scheduled Monday, as were flights to destinations in Africa, South America and Asia. «Usually we have 1,800 flights a day,» Deutsche Lufthansa AG said early Monday. «For today, we foresee about 1,000 flights planned, but there may be more flights that could be canceled during the day,» the airline warned. It offers some 160 long-haul flights to destinations worldwide. The airline, Germany's largest, estimated the strike could cost it some ¤25 million ($34 million) per day. Pilots for Lufthansa Cargo and the low-budget subsidiary, Germanwings, are also taking part in the strike.