Wildlife officials said one elephant was run over by a passenger train in the island's northeast, while two others were found shot dead in the central and eastern regions.

Elephants are protected by law and considered sacred due to their significance in Buddhist culture, but farmers often kill them to protect their crops.

Human-elephant conflict in Sri Lanka has resulted in the deaths of nearly 200 elephants and 55 people so far this year.

"We have launched investigations into the shootings of the two elephants, it looks like the work of local farmers," a police spokesman in the capital Colombo said.

The train accident occurred in Gallella, the same area where seven elephants were killed by a locomotive in February, the worst incident of its kind in Sri Lanka.

It happened despite speed limits on trains passing through elephant-inhabited forest areas.

A Sri Lanka railway official said an "internal investigation has been launched to establish if the driver had violated the speed limit".

Wildlife authorities released six elephants, aged between five and seven, back into the jungle on Thursday after rehabilitating them under a conservation programme that began in 1998.

The Elephant Transit Home in Udawalawe, about 210 kilometres (130 miles) southeast of Colombo, cares for rescued animals and eventually returns them to the wild.

The sanctuary is a major tourist attraction and holds 57 elephants that had been abandoned, injured, or separated from their herds.

Sri Lankan authorities believe the transit home's strategy of rewilding rescued elephants, rather than domesticating them, has been successful.

The home has returned 187 elephants to the wild since 1998.

Conservation efforts have become increasingly urgent due to the escalating conflict between wild elephants and farmers.

Official figures from Sri Lanka's wildlife department show that 4,835 elephants and 1,601 people have been killed in the worsening conflict since 2010.