Thomas Cook's summer bookings fell as security concerns meant more people opted for breaks in Spain over Turkey, Tunisia and Egypt, outstripping its efforts to adjust flights.

Despite shifting 1.2 million airline seats from the eastern to the western Mediterranean, the British travel operator said bookings were down by 5 percent and full-year profit would now be at the bottom end of market forecasts.

Chief executive Peter Fankhauser said Turkey, its second most popular destination last year, had not recovered as he had hoped after an attack on tourists in Istanbul in January.

"This has had a particular impact on our German airlines business, which is the market leader into Turkey."

The last update from Thomas Cook in March, came on the same day as explosions in Brussels. Fankhauser said bookings in Belgium had come "to a standstill" as a result.

Thomas Cook shifted airline seats from Turkey, Tunisia and Egypt to the Canaries, Balearics and mainland Spain where it had found extra hotel rooms, but it was not enough to compensate.

Customers could turn to Turkey at the last minute, Fankhauser said. "There is no late market in Spain, because Spain is filling up extremely fast, and then there may be a shift back into Turkey," he said.

Thomas Cook's rival TUI said earlier this month its bookings were up 1 percent, with demand strong.

"We are suffering a bit more (than rivals) because we are much bigger (in Turkey) than other competitors," Fankhauser said. "We are happy with the demand outside Turkey, we are up 6 percent if you take Turkey out."

Thomas Cook said operating profit for its year to end-March 2017 would be between GBP£310 million and GBP£335 million.

First half revenue grew slightly to GBP£2.67 billion, it said, and an underlying operating loss narrowed by 5 percent to GBP£163 million due to an improvement in margins.

It said it continued to expect to pay a dividend this year.