An investigation has been launched after four horses died during one single meeting in East Lothian.

The British Horseracing Authority will inspect Musselburgh Racecourse after Leather Belly, Smart Ruler, Sierra Oscar and Kensukes Kingdom lost their lives on Monday.

The winner of the first race, Kensukes Kingdom, was badly lame at the finish and was subsequently destroyed.

Smart Ruler collapsed and died, whilst two others, Sierra Oscar and Leather Belly, both broke their legs with fatal consequences.

Bill Farnsworth, who works at Musselburgh Racecourse, said: "I am absolutely confident the track is as safe as it possibly could be and this is just a case of four rare occurrences all happening on the same day at the same place.

"It's distressing for everybody concerned.

"The people involved in horseracing, the thing that we dread most is fatalities.

"It is regrettable that in competitive sport there will be injuries and sadly a very, very small number of fatalities."

Campaigners have now called for a review of horses' welfare following the event.

Libby Anderson of OneKind said: "Can you justify putting horses at risk and the amount of suffering that has been caused.

"This is a particular tragedy and it focuses our attention because it was four horses in a day.

"But one horse at a race meeting is not uncommon."

A BHA spokesperson said: "The incidents at Musselburgh were extremely distressing for everyone involved in the sport, not least for the owners of the horses and the trainers and stable staff who cared for them through their lives.

"For four horses to be fatally injured on one day of racing is very rare.

"Owing to the sport's investment in welfare research and education and ongoing programme of innovation and improvement, the average fatality rate in Britain over the last few years has reduced to around 0.2% of runners.

"Everyone in British racing is committed to reducing risk and making racing safer for our participants.

"As the sport's independent regulator we obviously treat issues such as this very seriously and work will now be undertaken to identify if there are any risk factors at the course or with the horses that might have contributed to these incidents.

"We will work with the racecourse, and the BHA's inspector of courses will be visiting Musselburgh in the coming days to carry out a full inspection.

"Where appropriate some of the horses are also being sent for post-mortems to establish more information, including for one of the horses whose death seems to relate to a sudden collapse."

Musselburgh Racecourse posted a statement on Twitter following the incidents.

A spokesperson wrote: "We can confirm that following unfortunate incidents yesterday, four fatal injuries occurred.

"Our thanks go to the veterinary team for their immediate assistance, and our condolences go to all connections."