By Subir Bhaumik
BBC News, Calcutta
Soldiers are helping to enforce a curfew in a strife-hit region of India's north-eastern Meghalaya state after police shot dead 12 protesters.
Police say they opened fire on Friday when students attacked them with stones but protesters say it was unprovoked.
The state's home minister has rejected opposition calls to resign.
Students from the Garo tribe have been staging protests against planned educational reforms that have created divisions with the Khasi tribe.
Troops have been carrying out high-profile marches in the Garo Hills region after being called out on Friday to help restore order amid an indefinite curfew.
State Home Minister Mukul Sangma refused to concede to opposition demands for his resignation.
"It is a sad incident , but why should I resign? I did not ask the police to shoot at the boys. It all happened on the spur of the moment," Mr Sangma said.
The most notable politician from Garo Hills, India's former parliament speaker Purno Sangma, said the entire Congress government in Meghalaya should resign.
"The police used AK-47 assault rifles on a peaceful gathering. These were students who might have thrown a few stones, but the police reaction was clearly brutal," Purno Sangma told the BBC.
He threatened to resign his parliament seat and said legislators of his Nationalist Congress Party in Meghalaya would resign theirs if the government did not.
The protests took place in the towns of Tura, in West Garo Hills, and Williamnagar, in East Garo Hills.
The deputy inspector general of the Garo Hills range, Vijay Kumar, told the BBC from Tura that the Garo Students Union (GSU) was not given permission to hold a rally.
Despite that, he said hundreds of people gathered in Tura for the rally.
When the police arrived, the crowd threw stones injuring some policemen, he said.
The police and paramilitary soldiers then opened fire in retaliation, Mr Kumar said. He said seven people died in Williamnagar and five in Tura.
Overstone Marak, a spokesman for the Garo Citizens' Committee, the organisation jointly leading the protest campaign, said: "Police opened fire on the agitators without any provocation and without resorting to baton charging first - which is the normal practice."
The GSU began a campaign of protests earlier this month against the state government's proposed educational reforms.
The government has asked the student body to end its protest actions before it negotiates over the reforms.