Two Britons are dead and two others are in hospital after a hot air balloon crashed near the Egyptian city of Luxor, travel group Thomas Cook says.
Reports suggest 18 people were killed, with French, Hong Kong and Japanese nationals also among the dead.
The balloon was at 1,000 ft (300m) up when it exploded, caught fire and plunged on to agricultural fields west of Luxor, officials said.
Thomas Cook said the accident was a "terrible tragedy".
The four Britons had been on holiday with the tour operator and were among more than 20 people in the balloon when it crashed to the ground in flames.
Thomas Cook said it was working closely with the Foreign Office and the authorities in Egypt. It has about 150 customers in the Luxor area at present.
The Foreign Office said its staff in Luxor were in "close contact with the Egyptian authorities and are providing consular assistance".
Thomas Cook has set up an emergency phone line for concerned relatives on 0800 107 5638.
"We can confirm that two of our guests are in local hospitals, but tragically two of our guests have died in the hot air balloon incident in Luxor, Egypt this morning," the company said.
Thomas Cook UK and Europe chief executive Peter Fankhauser added: "The thoughts of everyone in Thomas Cook are with our guests, their family and friends.
"We have a very experienced team in resort with the two guests in the local hospital, and we're providing our full support to the family and friends of the deceased at this difficult time."
The crash happened on one of the many dawn hot air balloon flights that give tourists a view of Luxor's tourist attractions, such as Karnak temple and the royal tombs in the Valley of the Kings.
Thomas Cook said it had temporarily suspended sales of hot air balloon rides in Egypt.
The balloon's operating company, Sky Cruise, confirmed that a gas cylinder had exploded on board the balloon, bringing it down.
Holidaymaker Cherry Tohamy was in another balloon that was landing when she heard an explosion and saw flames from a balloon above.
She told the BBC: "Our pilot told us that the balloon had hit a high pressure electrical cable and a cylinder on board exploded. People were jumping out of the balloon from about the height of a seven-storey building."
She added that ambulances had arrived at the scene within 15 minutes.
Hot air balloon crashes have happened in Luxor before. Two British women were among 16 injured when their balloon came down after hitting a communications tower in April 2009.
Balloons were grounded for six months after that crash while safety measures were tightened and pilots were re-trained by Egypt's Civil Aviation Authority.
Linda Lea, 67, a retired policewoman from Stoke-on-Trent, who had four months of hospital treatment after the 2009 crash that left her with 26 broken bones, said the latest incident brought back painful memories.
"It's the opportunity. You've got to see the whole spectrum and the whole vista of the Valley of the Kings," she told the BBC as she digested news of another crash.
"If you're interested in Egyptian history it's a unique opportunity to do that."
The balloon Mrs Lea flew in hit a mobile phone mast, ripping the balloon and causing an explosion that brought it crashing down. Fire also brought down the balloon in Tuesday's Luxor crash.
"These balloons are just too unstable. There is not enough training of staff. There were about 22 or 23 in my balloon when it crashed and maybe there was too many then and too many in today's accident," she said.
Mark Packer, from London, who went on a balloon in Luxor earlier this month, said he was left "scared" by his experience.
He said the pilots did not appear to treat the equipment carefully and his flight hit a tree.
"They go up to 800 or 1,000 feet, then bring the balloon down and across the temples at a low height," he told the BBC.
"I'm not saying they're not experienced pilots, but they are dragging the baskets through the sugar canes... The pilot broke off a piece of sugar cane to give to us."