Officials at the RSPCA (Royal Society for the Prevention of Cruelty to Animals) have described the six equine fatalities at the Cheltenham Festival this week as "extremely concerning".
There were four deaths on the final day, with three of them - Dresden, North Hill Harvey and Some Plan - coming in the concluding race, the Johnny Henderson Grand Annual Challenge Cup Handicap Chase.
Earlier in the day, Katie Walsh was unshipped from Sandsend before the last in the County Hurdle and it was later confirmed the Willie Mullins-trained runner had suffered a fatal injury. The two other equine fatalities took place on Tuesday's opening card with the deaths of Mossback and Report To Base.
The British Horseracing Authority said on Friday evening it would be reviewing the circumstances leading to the fatalities and examining evidence from the week before deciding how to proceed.
Urging a "comprehensive review", David Muir, horse racing consultant at the RSPCA, said in a statement: "We are deeply saddened that six horses have died at the 2018 Cheltenham Festival.
"These fatalities are extremely concerning and it is essential that the announced review by the racing industry must be completely comprehensive to reduce the likelihood of such tragedies occurring again.
"The review should be inclusive of horse welfare organisations and for the benefit of the horses it is essential that we continue to work with the regulatory body giving our full support to their review. A review was carried out at Aintree in 2012 which has since reduced horse falls, injuries and fatalities.
"We also believe the use of the whip and the term encouragement needs to be clearly defined, and our view is that the whip should only be used for safety and correction.
"The deaths of Mossback and Report To Base on Tuesday and Sandsend, North Hill Harvey, Dresden and Some Plan yesterday (Friday) are extremely distressing and our thoughts are with all those involved."
BHA media manager Robin Mounsey confirmed talks are planned with all relevant parties, including the RSPCA.
He said: "We will be meeting next week to discuss how we are going to proceed with the review of the Festival, but as part of this process we will be consulting with relevant stakeholders, which includes recognised welfare organisations such as the RSPCA and World Horse Welfare."
World Horse Welfare has welcomed the planned BHA review and believes it is "vital" to thoroughly investigate all fatalities.
A statement read: "World Horse Welfare is very concerned that six horses have died at the 2018 Cheltenham Festival.
"The deaths of Mossback and Report To Base on Tuesday, and Sandsend, North Hill Harvey, Dresden and Some Plan on Friday must be extremely distressing for all those involved. None of these fatalities can be accepted as a by-product of the sport.
"We acknowledge that racing will never be risk-free, but it is vital that any fatality is fully investigated and that wherever steps are taken to reduce the likelihood of such tragedies occurring.
"Given the number of fatalities at the Cheltenham Festival over the past few years, we are extremely relieved that the British Horseracing Authority have heeded our calls and pledged to undertake a detailed review of the Festival.
"We look forward to playing a part in this vitally important process; there is much to learn from 2011 Grand National review which made such a difference to the safety of horses."