At least 18 elephants have died in a forest in Nagaon district of Assam, seemingly due to a lightning strike, PTI reported. The incident took place on Wednesday night at a hill in the Kundoli proposed reserve forest in the Kathiatoli range, Principal Chief Conservator of Forest (Wildlife) Amit Sahay, told the news agency.

On Friday, Assam Forest Minister Parimal Suklabaidya visited the site. He said that an inquiry committee and a team of veterinarians has been set up. “The preliminary report of inquiry has been asked to be submitted within three days and a detailed investigation report within 15 days,” he tweeted.

On Thursday, Suklabaidya had said preliminary investigation found the elephants were killed due to electrocution caused by lightning, however the exact reason will be known once the post-mortem report comes, ANI reported.

Chief Minister Himanta Biswa Sarma’s office also expressed grief on the incident.

Some social media users, including Indian Forest Service officers, put the toll at 20-22. However, there is no official confirmation on these numbers yet.

According to a 2017 census, Assam, with 5,719 elephants, has the second highest population of the animal among all states, after Karnataka, according to the Hindustan Times.