The owners of a giant rabbit named Simon who was found dead after a United Airlines flight demanded on Monday that the airline pay damages, order an outside investigation and re-evaluate how it handles animals on flights.

Attorneys for Simon's owners, who purchased him in hopes of winning the title of world's largest rabbit at the Iowa State Fair this summer, said they would take legal action if United failed to respond within seven days.

The lawyers claim it is possible the 3-foot-long (one metre) hare died after being placed in a freezer for 16 hours upon landing in Chicago on a flight from London. They claim the airline then destroyed his remains without permission.

"United Airlines can issue any statement they like but their company's credibility is under question when they immediately cremate the giant rabbit Simon without anyone's consent," said Guy Cook, lead attorney for the three-person investment group that owned the rabbit. "They destroyed the proof."