NEW DELHI (Reuters) - Protesters led by India’s lower-caste Dalit community on Monday set fire to police posts and blocked railway tracks as they opposed a Supreme Court ruling that bars immediate arrest of individuals accused of discriminating against them, media said.

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Dalits are at the bottom of India’s ancient caste hierarchy and form about a quarter of the population. Some protesters carried banners demanding a nationwide shutdown, while others held placards saying the judgment was diluting the law.

“Get out in strong numbers, block the roads if needed, but do not touch public property,” Jignesh Mevani, an independent Dalit lawmaker from the western state of Gujarat, told the India Today news channel.

Although he backed the protests, Mevani said, he was opposed to any damage to public property.

Television showed images of police beating protesters and an unidentified person firing shots, with demonstrators in the northern state of Haryana also setting police posts ablaze and attacking shops.

Four people were killed in the central state of Madhya Pradesh, where police imposed a curfew and blocked internet services in some places, television showed.

Shops were shut as protesters blocked key roads in many areas, including the capital, New Delhi, and the industrial city of Ahmedabad in Prime Minister Narendra Modi’s home state of Gujarat, the paper added.

Last month, the Supreme Court ruled that arrests under a law meant to speed action on complaints of violence against Dalits required prior sanction from officials, and barred the immediate arrest of those accused in such complaints.

In its judgment the court said prior approval was required following the acknowledged abuse of provisions for arrest in such cases.

By the end of 2016, about 90 percent of roughly 145,000 cases involving Dalits were still awaiting trial, government data from last year showed.

Investigation showed that fewer than a tenth of the cases brought by Dalits in 2016 were proved false, according to government data.

Modi’s government on Monday submitted a review petition to the court, asking it to amend the judgment, Home Minister Rajnath Singh said in a televised interview.

Hindus, who account for more than 85 percent of India’s population of 1.3 billion, were traditionally grouped into thousands of castes, whose membership was determined by birth.