MANILA (AFP) - A South Asian turtle famed for its polka dot skin is under growing threat of extinction as demand for it as an exotic pet booms, a wildlife monitoring group warned on Friday.

Hundreds of the black spotted turtle are regularly discovered at airports around Asia, having been illegally smuggled in luggage aboard commercial passenger flights, Traffic said.

Some are little bigger than a hand, but they can sell for thousands of dollars on the black market.

"Illegal international trade of the black spotted turtle in Asia has escalated over recent years and immediate action is required to stem the flow," Traffic said as it released a report on the reptile's fate.

The turtle, also called the black pond turtle, is found in the rivers of Bangladesh, India, Nepal and Pakistan. It is regarded as one of the most attractive turtles because of its spotted skin and boldly patterned shell.

The International Union of Conservation and Nature lists it as vulnerable, one step away from endangered, and Traffic said the sudden rise in demand for the turtle as a pet in other parts of Asia had made its future much more fragile.

In the most recent seizure, 230 turtles were found in unclaimed bags at Bangkok's main international airport on May 14, according to Traffic. The luggage had been on a flight from India.

Since January last year, authorities around the region have seized more than 2,000 turtles, with most of the busts occurring in Bangkok, Traffic said.

It said Bangkok was regarded as a transit hub, with the turtles then flown to Hong Kong, Taiwan and other places in East Asia where there was high demand for them as pets.

A mature turtle that is about 30cm long can cost more than US$2,000 in Hong Kong, according to people who follow the trade.

Many turtles around the world are seriously threatened, with those in Asia particularly at risk due to their habitats being destroyed or damaged and demand for them as pets or food.

Seventeen of the 25 most critically endangered tortoises and freshwater turtles on the Iucn's Red List are in Asia, according to Traffic.

Traffic said it sounded the alarm on the black spotted turtle because of the alarming rise in seizures in recent years and to call for tougher action by authorities.

It said, despite laws in place, people were rarely prosecuted when caught smuggling the turtles.

In rare cases of prosecution, one Thai man was sentenced to three months jail in Hong Kong and another man jailed for seven months in Taiwan.