NEW DELHI, June 3 (Xinhua) -- At least 20 people were killed in clashes between police and land encroachers in the northern Indian state of Uttar Pradesh Thursday, said police Friday.

The violence took place in Mathura city of the state Thursday during an anti-encroachment operation by police, according to Superintendent of Police Mukul Dwivedi in Lucknow, the state capital of Uttar Pradesh.

While 250 people have been detained for their involvement in the incident, the city continues to be tense even as heavy police reinforcement has been deployed in the violence hit region, according to Indo-Asian News Service.