Audio clip in Malayalam urging attacks at religious gatherings in India appears

An audio clip, purportedly from an Islamic State in Iraq and Syria (ISIS) fighter, has surfaced, with a message that encourages sympathisers to carry out attacks at religious gatherings.

Its discovery has raised fears of lone-wolf attacks in the South Asian country.

The clip in Malayalam, the language spoken in the southern state of Kerala, calls for Las Vegas-type terror attacks at crowded and popular festivals such as the Kumbh Mela and Thirssur Pooram, said reports in the Indian media.

A Kerala district police chief said they are trying to ascertain if the 10-minute clip is related to the arrest of five ISIS sympathisers last month in Kannur, one of 14 districts in the state.

The Kumbh Mela, the world's largest religious gathering with tens of millions of pilgrims turning out to take a holy dip in the river Ganges every four years, will next be held in 2019.

The Thirssur Pooram, a popular annual Hindu temple festival held in Kerala, will take place in April.

A Kerala police official said the clip is being investigated by state and federal law enforcement and intelligence officials.

It came to the notice of authorities as it was being shared on multiple WhatsApp groups in Kerala. Media reports say it features a man's voice, saying, "Use trucks. Drive over them at Thirssur Pooram or at Maha Kumbh Mela. Islamic State Mujahideen are doing it in several parts of the world. In Las Vegas, one of our supporters killed many people at a music concert."

The American gunman had shot dead 58 concert-goers last month.

Kerala, where 26 per cent of the population is Muslim, is among India's more prosperous states. It scores high on all social indicators, from education to healthcare, and has 2.5 million people working in the Gulf nations who send back thousands of dollars in remittances every year.

Religiously diverse, it has seen a more conservative strain of Islam emerging in the last few years.