Clashes between Indian police and followers of a revolutionary sect have left at least 23 people dead after an operation to evict thousands of people from parkland erupted into violence, officials said Friday.

Two police officers were among those killed in the overnight clashes during a move to expel around 3,000 sect followers who had illegally occupied public land in the city of Mathura for the last two years.

Police and other officials said they came under fire from armed members of the sect who positioned themselves on tree-tops and also hurled crude explosive devices at them.

"Twenty-three people, including two police officers, died in the clashes," divisional commissioner Pradeep Bhatnagar, who is the top civilian official for the area, told AFP.

"Eighty are injured, including 30 policemen. Most of them have bullet wounds and are in critical condition.

"Twenty-one of the dead were extremists who attacked police and civil authorities with arms and bombs from inside the park.

"They were carrying automatic rifles and crude bombs and had fortified the area in a military style."

A senior officer said police were forced to respond with live fire after two of their men were shot dead by followers of the sect, which is known as Swadhin Bharat Vidhik Satyagrah.

One of them was a police superintendent, the most senior officer in Mathura which is located in the northern state of Uttar Pradesh, around 150 kilomters (90 miles) east of the capital New Delhi.

"We had gone to clear the area but were fired upon by the miscreants. Two of our men died," Hari Ram Sharma, inspector general of police for Uttar Pradesh, told AFP.

More than 1,000 followers of Swadhin Bharat Vidhik Satyagrah were arrested, Sharma added. The area has now been sealed off and the situation was tense but under control.

The clearance operation was launched after authorities won a court order to remove hundreds of tents and makeshift wooden structures from a 270-acre (109-hectare) patch of land that the sect had been occupying since late 2014.

Television images and pictures from the scene showed that many of the huts where members of the sect had been living had been set alight, with smoke billowing across the area.

In postings on social media, Swadhin Bharat Vidhik Satyagrah's followers describe themselves as political and social revolutionaries. Their demands include the abolition of elections and cheaper fuel for everyone.

"Their ideology is similar to the Naxalites," said Bhatnagar in reference to Maoist revolutionaries in parts of eastern and central India.

"They want to free India from the present governance system including the abolition of the post of prime minister and president."

Swadhin Bharat Vidhik Satyagrah is led by a man called Ram Vraksha Yadav, whom police say was at the scene of the violence in Mathura but has so far eluded arrest.

In 2014, hundreds of armed supporters from another sect clashed with police in the northern state of Haryana during a raid to arrest their leader who faced murder allegations. At least six people died in the violence.