At least five elephants were killed by lightning in a West Bengal wildlife reserve, officials said Friday.

The animals died Thursday in a tea estate under the Buxa Tiger Reserve area in the state's northern region.

Their carcasses were found by tea garden workers on the bank of a river near the New Lands Tea Estate in Alipurduar area of Jalpaigur district, 700 km north of Kolkata.

'We suspect that the elephants died of lightning when they came to drink river water. There were no external injuries or evidence that the elephants were poisoned or electrocuted by poachers,' Buxa reserve official Subhankar Sengupta told IANS.

However, he added that the exact cause of death could only be ascertained after the post-mortem reports were available.

'This seems to be a case of death from lightning, which is very rare. Perhaps it occurred because the elephants were in a river bed and there were no trees around to protect them from lightning,' said Animesh Bose, an official of the Himalyan Nature and Adventure Foundation (HNAF) in Siliguri.

Shakti Ranjan Banerjee of the Wildlife Protection Society of India (WPSI) agreed that the cause could be lightning.

In the last two years, at least 12 elephants were killed either in accidents on the Dooars railway track or by poaching and electrocution in the northern region of West Bengal.

Expressing serious concern over the elephant deaths, West Bengal Forest Minister Ananta Roy said the forest department should probe the unnatural deaths.