At least four people have died in violence in a northern Indian state after authorities demolished a mosque, alleging it was constructed illegally.

Violence broke out in Uttarakhand's Haldwani town during what police say was an "anti-encroachment drive".

Authorities said the drive was launched to clear illegal constructions, including the mosque and an adjoining madrassa (religious school).

But Muslims who prayed at the mosque say they have been unfairly targeted.

Hundreds of protesters and police personnel were injured in the clashes which broke out on Thursday evening.

Videos showed protesters setting fire to vehicles and pelting stones and the police firing tear gas at them.

A curfew has been imposed and the state has issued "shoot at sight" orders to bring the situation under control.

The incident took place in Banbhoolpura area of Haldwani. The district had witnessed widespread protests in January last year after more than 50,000 people, mostly Muslims, were served eviction notice alleging they were illegally living on land owned by the Indian Railways. The demolitions were later stayed by India's top court.

Officials said the latest action was based on a high court order asking authorities to clear illegal settlements from the area.

District Magistrate Vandana Singh said the mosque and the madrassa were demolished because they were illegally built on government land and were not registered as religious structures.

"The drive was not targeted towards any particular community. It began peacefully but a mob attacked officials soon after, leading to violence," Ms Singh said, adding that authorities had given the mosque's administration prior notice about its demolition.

Locals have denied this and said the mosque was demolished before the court could give a final decision in the case.

"When the administration came [to demolish the structures] we asked them to stop until the next court hearing. But they did not listen. If they had waited for the final decision of the court, there would have been no resistance [from us]," Shakeel Ahmad, a local councillor, told the Indian Express newspaper.

Tensions over demolitions of mosques have risen in the past few months.

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