Ten endangered Asiatic lions have died in the last two weeks in India, authorities confirmed on Tuesday, four of them from a virus that killed around 1,000 lions in Tanzania in the 1990s.

The new deaths take the toll at the Gir sanctuary in the western Gujarat state, home to India's entire population of around 500 wild Asiatic lions, to 21 since September.

India's National Institute of Virology determined that the canine distemper virus was responsible for four of the 10 latest deaths, Gujarat environment minister Ganpat Vasava told AFP.

In 1994, an outbreak of CDV — which can spread from dogs in the wild — killed around 1,000 lions in Tanzania's Serengeti National Park.

While six of the latest 10 deaths were from a parasitic infection caused by ticks, the four CDV deaths have prompted authorities to run further tests on the 11 lions that died last month, according to D.T Vasavada, Gujarat's chief conservator of forests.

“A team of experts is working to ascertain the reason for the viral infection. Since all 21 lions have died in one Sarasiya grassland, it is a matter of concern,” Vasavada added.

Local officials said another 31 lions from the same part of the sanctuary are being kept under medical observation, though they have not shown any signs of illness so far.

According to the last count in 2015, there were 521 Asiatic lions in the Gir sanctuary, which is spread over 1,400 square kilometres.