Zoos in Britain should be brought under a "centralised licensing" system, an animal charity has said following the deaths of two tigers in the last week.
A female tiger at London Zoo was killed by a potential mate and another died after tigers fought at a safari park.
The Born Free Foundation says the zoo licensing rules currently overseen by local authorities have "differences in understanding and application".
The zoo trade body says the tiger deaths were unrelated to licensing.
The Born Free Foundation, which campaigns to keep wildlife in the wild, says that "significant incidents occur with disturbing frequency" at zoos.
The charity's head of animal welfare and captivity, Chris Draper, says "licensing and inspection of zoos in Britain is currently the responsibility of the large number of local authorities".
This leaves the law "open to interpretation", he said.
'Important conservation work'
The professional body which represents more than 100 zoos and aquariums says it was "saddened to hear of the deaths of two female tigers at two of its member collections in recent days".
But the British and Irish Association of Zoos and Aquariums (BIAZA) rejects Born Free's call for changes to licensing, saying the events must not overshadow the important conservation work undertaken by its members.
"BIAZA welcomes robust zoo licensing and endorses recent steps taken by Defra [Department for Environment, Food and Rural Affairs] to strengthen the zoo licensing process in the UK," a spokeswoman added.
An endangered female Sumatran tiger was killed by a potential mate during their first introduction at London Zoo on 8 February.
The zoo said staff used air horns and fire extinguishers to stop the male tiger, Asim, from killing Melati.
However, despite the best efforts of the vets, 10-year-old Melati died.
On Monday, a rare Amur tiger died in a fight with two other tigers at Longleat Safari and Adventure Park in Wiltshire.
The park said 13-year-old female Shouri was killed after gaining access to a paddock where two other tigers, Red and Yana, were being held. A fight took place between the three animals.
The park said a full investigation was ongoing to determine the exact circumstances surrounding the "terribly sad event".
There are thought to be only 300 Sumatran tigers and 540 Amur tigers left in the wild.
A spokesperson for the Department for Environment, Food and Rural Affairs, said: "The UK has some of the highest animal welfare standards in the world.
"The current licensing regime for zoos is enforced by local authorities, but they are regularly inspected by trained professionals against our high standards.
"These standards are developed together with leading animal welfare experts on our Zoos Expert Committee."