Hundreds of security forces patrolled a west Nepal area Tuesday where ethnic protesters, demanding statehood, attacked police with spears and knives a day earlier leaving at least six officers and three protesters dead and many others injured.

A curfew was imposed and policemen and soldiers were rushed to Tikapur, 400 kilometers (250 miles) west of Kathmandu, where the clashes happened Monday.

Government administrator Raj Kumar Shrestha said authorities were in control of the town and surrounding areas and there were no protests or reports of curfew violations.

At least 20 policemen were being treated in hospitals after being hurt in the clashes.

It was not clear if other protesters were also killed as many fled into the jungle and nearby villages after the troops were called into the townLocal news reports said it could be as high as 20.

New York-based Human Rights Watch called on the government to order an independent investigation into the deaths and said the security forces must respect basic rights.

"The violence ... and the deployment of the army threatens to further increase tensions in an already charged situation," the statement quoted Brad Adams, the group's Asia director, as saying.

Home Minister Bam Dev Gautam told the Constituent Assembly, the national parliament, that the protesters surrounded police who were enforcing a curfew in Tikapur, about 250 miles west of Kathmandu. They attacked the officers with stones, knives and spears, and one was set on fire and died, he said.

Police from neighboring districts were rushed to the town as reinforcements. The government also deployed soldiers to bring the situation under control, Gautam said.

The protesters from the Tharu ethnic group are demanding a separate state in the new constitution, which is being finalized in the Constituent Assembly. They have organized general strikes and street demonstrations in recent days, but the protests turned violent Monday.

Nepal has been governed by an interim constitution for years now. A Constituent Assembly elected in 2008 failed to draft a new charter in four years, and a second assembly was elected in 2013. Disagreements among political parties have been blamed for the delay.

Since an earthquake in April that killed thousands of people, there has been pressure on politicians to speed up the drafting process.

The main political parties now agree that there should be seven federal states, but smaller political parties and ethnic groups oppose either the number or makeup of the states.

The Associated Press