NEW DELHI - A firebrand protest leader vowed Sunday to spread agitation over caste preferences nationwide, just days after the worst violence in more than a decade in western India left nine people dead.

Hardik Patel said he was gathering support to hold protests in New Delhi and the northern city of Lucknow, after arriving in the national capital to meet leaders of various castes in India's rigid social hierarchy.

"We will take the movement all over the nation and turn it into a country-wide movement," the 22-year-old self-styled leader told reporters after landing from the western state of Gujarat.

"This is going to be a long fight."

India was forced to call in the army on Wednesday following riots and arson across Gujarat after a mass rally in the state's main city of Ahmedabad turned violent.

Patel, who was briefly arrested, led the rally of an estimated half a million people demanding special treatment for the Patidar or Patel caste.

The Patidars are one of the state's most affluent communities, but they say they are struggling to compete with less privileged castes for government jobs and university places.

India sets aside a proportion of jobs and places for Dalits, known as "untouchables", and for other so-called "backward castes" and tribals under measures intended to bring victims of the worst discrimination into the mainstream. But the policy of "reservation" causes resentment among other communities who say it freezes them out. "Due to reservations, the country is 60 years behind. The government needs to give reservations to all the needy communities," Patel said on Sunday.

Local media said it was the first time the army had been deployed in Prime Minister Narendra Modi's home state of Gujarat since communal riots in 2002 left at least 1,000 people dead.

Modi appealed for calm immediately after last week's violence. The scale of the protest movement appears to have taken political leaders by surprise, after beginning earlier this year and rapidly gathering pace in recent weeks.

Meanwhile, Indian Prime Minister Narendra Modi will let an executive order making it easier for businesses to buy land lapse on Monday after failing to win support from opposition parties in a major blow to his economic reform agenda.

Modi said on Sunday the government was ready to amend the proposed law and criticised the spreading of false rumours that made farmers afraid of the changes.

"I have always said that, in the dispute related to the land acquisition law, the government is open minded," Modi said in his monthly radio address. "I am willing to accept any suggestion for the benefit of farmers."

Modi swept to power last year on expectations he would accelerate an economic transformation that began in the 1990s but is struggling to build support for reforms in parliament, where his party is in the minority in the upper house.

Leaders of Modi's party said they had not given up on making it easier to acquire land needed to kick-start hundreds of billions of dollars in stalled projects. However, after failing to win support in parliament, they may ask states to pass their own laws.

Modi has had to issue temporary executive orders in the past seven months that allow the government to forcibly purchase farmland for industrial development. He has failed to secure the votes in parliament needed to make the changes permanent.

Land reform is critical for Modi's drive to build new roads, homes and factories and, if stalled, would blight his vision of 100 new 'smart' cities across India linked by industrial corridors and high-speed rail routes criss-crossing the country.

Conflict between farmers and companies trying to secure land for industrial projects has hampered India's plans to expand its network of highways, build mines and other infrastructure, holding up about $300 billion of investment.