The Indian army patrolled riot-hit areas of Prime Minister Narendra Modi's home state of Gujarat on Thursday after the death toll rose to seven in two days of caste-related violence.

Clashes spread after police arrested a young leader of the influential Patel clan who led a huge rally on Tuesday to demand more government jobs and college places for members of his community.

The breakdown of law and order revived memories of serious rioting in 2002 in which more than 1,000 people, most of them Muslims, died. Modi, chief minister of Gujarat at the time, has faced criticism for doing too little to halt the bloodshed.

"Six protesters and a police officer have lost their lives and 18 people are critically injured," said Keshav Shah, a senior police officer in the state capital Gandhinagar.

"Schools, business and private offices will not open today. The mood is tense and no one should venture out," he said, adding that a curfew would remain in force.

Modi has called for calm in the state that he ran for more than a decade before leading his nationalist Bharatiya Janata Party (BJP) to victory in last year's general election.

The Patels, or Patidar community, make up 14 percent of the population in Gujarat. A relatively affluent group of land- and business-owners, they had been a bulwark of support for Modi.

Members of the Patel community said they will continue to demand changes to policies that, they argue, unfairly favor groups at the lower end of India's social order.

"We will not let the government suppress our demands. They can kill as many Patels as they want," said 21-year-old activist Hardik Patel.

The young leader drew a crowd of half a million to a rally on Tuesday in the city of Ahmedabad. His detention there led to clashes between police and protesters across the state, forcing authorities to release him.