Demonstrators armed with spears and axes have killed eight police officers in western Nepal during escalating protests against a proposed new constitution, officials say.
The government announced a curfew and plans to send in the army to Kailali district in the country's remote far west, where authorities said there were reports that three demonstrators may have also died in Monday's clashes.
"So far I can confirm that eight members of our security forces have been killed, including two paramilitary personnel," home ministry spokesman Laxmi Prasad Dhakal said.
"An indefinite curfew has been imposed in the area from 4pm today," Dhakal told AFP.
The violence erupted as police attempted to prevent protesters from entering restricted areas and from vandalising government offices in the town of Tikapur, 420 kilometres west of Kathmandu, Home Minister Bam Dev Gautam told parliament.
"All of a sudden protesters encircled the police and attacked them with knives, axes, sickles and spears," Gautam said.
He said demonstrators also set fire to one of the paramilitary officers - although it was unclear if he survived the attack.
"Inspector Ram Bihari Tharu of the Armed Police Force was burnt alive," he said.
More than 40 security personnel were injured in the clashes and were taken to Tikapur hospital, district chief Raj Kumar Shrestha said.
Another official, deputy district chief Udaya Bahadur Singh Thakuri, warned that the death toll could rise.
"We have heard reports that... three protesters have also been killed, we are trying to confirm the details," he told AFP.
A new national constitution presented in parliament on Sunday aims to restructure Nepal as a federal state made up of seven provinces and draw a line under a decade-long civil war that ended in 2006.
But protesters argue that the new internal borders will discriminate against historically marginalised communities including the Tharu ethnic minority, which has struggled to overcome decades spent as bonded slaves to high-caste landowners.
The latest clashes broke out when Tharu members held a protest to demand their own separate province.
Minister Gautam said the government would send troops to the area to try to bring the situation under control, and appealed for peace.
"At a stage when we are heading to a new era... we must call on people to not be involved in activities that disturb social harmony and ignite ethnic hatred," Gautam told MPs.