Eleanor Brennan, one of Britain's most promising three-day eventers, was killed on Saturday when her horse landed on top of her at the Florida International Three-Day Event at Ocala.

The 21-year-old was competing in the cross-country event when her mount, Mr Barnabus, stumbled at a jump and left the rider with head and chest injuries. Organisers confirm Brennan died later at Munroe Regional Medical Center, in Florida. Her horse also sustained fatal injuries.

Brennan, who lived and worked in Virginia, was once the youngest competitor at the Badminton Horse Trials. A good friend of Zara Phillips, she spent several years training in Gloucestershire with Zara's father, Captain Mark Phillips, before studying equine business management at Hartbury College.

""It is always tragic when something like this happens," said Yogi Breisner, manager of the British equestrian team. "My condolences go to her family and friends. She was a lovely, charming young lady and a good rider."

Tom Warriner, chairman of the Florida Horse Park, said: "It's a tragic experience for all of us". Brennan's death was the second tradegy to occur at the venue, following the death of a rider in 2006.

Organisers plan to review tapes of the incident.

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