At least 24 people have been killed and 40 others injured during clashes between police and squatters in the northern Indian town of Mathura.
Clashes broke out on Thursday as police tried to evict several thousand former members of a religious sect who had occupied a public park for two years.
Two senior police officers were among those killed overnight.
Akhilesh Yadav, the chief minister of Uttar Pradesh state, has ordered an inquiry into the violence.
"At 5pm on Thursday, a police team visited Jawahar Bagh park for a recce following a court order to evict the squatters," state police chief Javed Ahmed told a news conference.
"The protesters fired at the policemen without any warning or provocation. They also pelted the team with stones. Two senior police officers were killed in the attack."
Many unanswered questions - Vineet Khare, BBC Hindi in Mathura
There is shock in Mathura. Outside Jawahar Bagh, the park where the violence took place, there are now just media and security personnel. Access to the large area of land where thousands squatted for more than two years has been barred.
A senior state government official had tears in his eyes describing the violent deaths of the two senior police officials - Mukul Dwivedi and Santosh Kumar Yadav. There are many unanswered questions too. For instance, how the squatters manages to bring such a large cache of arms and ammunition into the heart of the city without the knowledge of local intelligence units.
Not much is known about the group involved. A senior police official responsible for law and order, Daljeet Chaudhary, described them as anarchists who do not believe in the Indian system, or the legitimacy of its prime minister or president.
Police say they have arrested more than 300 people but they still have a lot of explaining to do.
He said more police teams were sent to the scene to bring the situation under control, and his colleagues retaliated after some of the protesters attacked them.
Mr Ahmed added that some of the protesters had died from bullet and other injuries sustained during the clash, but at least 11 were killed in a blaze caused by cooking gas cylinders.
More than 300 people have been arrested and the situation has been brought under control. Police have recovered a large number of firearms from the park, he said.
Who are the squatters?
Members of the Azad Bharat Vidhik Vaicharik Kranti Satyagrahi (Free India Legal Ideas Revolutionary Protesters) have been occupying Mathura's largest public park Jawahar Bagh for two years.
Reports say the group is headed by Ramvriksha Singh Yadav, but very little is known about him.
Members of the group earlier followed religious guru Baba Jai Gurudev, but since his death in 2012 some had started calling themselves "revolutionaries" and claimed to be followers of Indian independence hero Subhas Chandra Bose.
The group has been making radical demands such as declaring the Indian parliament and the posts of prime minister and president unconstitutional.
They also want the authorities to sell fuel at dirt-cheap prices. In their view 40 litres of petrol or 60 litres of diesel should cost just 1 rupee (about 1.5 cents; one penny).
Meanwhile, Twitter users in India have expressed anger over the incident, making Mathura one of the top trending topics.
Some Twitter users said politicians were trying to use the incident to criticise each other ahead of the state assembly elections in 2017.
And finally, Bollywood actress and Mathura MP Hema Malini has been criticised for tweeting about her upcoming film during a time of crisis in her constituency.