WASHINGTON (Reuters) - Delta Air Lines ( DAL ) on Friday asked the U.S. Transportation Department to allow it to delay resuming four daily flights to China, citing ongoing challenges in the market.

The U.S. air carrier currently operates daily flights to Shanghai from Seattle and Detroit, but asked for approval to not reinstate two other daily flights to Shanghai and two daily Beijing flights. Last week, United Airlines asked DOT for permission not to operate 6 of its 9 daily flights to China.