The planned mass Christmas Day conversion ceremony in India's Uttar Pradesh state has been banned by the state's police force.

Organised by an offshoot of the nationalist Rashtriya Swayamsevak Sangh (RSS) group, the 'ghar waapsi' or 're-conversion' ceremony for the Muslim-majority city of Aligarh was set to convert at least 1,000 Muslim and 4,000 Christian families from the Valmiki Dalit group, which the group claims to have identified already.

However, according to the Times of India, police spokesman Amit Agarwal said there were public order considerations and announced that the ceremony would not be given permission. "Under no circumstances will we allow the proposed mass conversation programme slated for December 25," he said, adding: "The so-called 'ghar waapsi' programme organised by the Dharam Jagran Samiti can become a law and order issue for the state and irrespective of the finer details of this event it cannot be allowed to be held."

The move, part of wider initiatives to convert Muslims and Christians – regarded as a 'return' to Hinduism by nationalist activists – had caused widespread anxiety among minorities and social commentators, who feared the impact on community relations in India's secular state. Campaigners say that converts at similar events have been bribed to change their religion, which is illegal under Indian law.

District magistrate Abhishek Prakash warned of the danger to inter-communal relationships, saying: "Religious conversion is a matter of personal choice and the law permits it. However, if certain groups deliberately try to provoke communal sentiments by misusing this provision, then we will certainly not allow this to take place."

Re-conversion ceremonies have hit the headlines recently with an RSS event in Agra. According to campaigners, the 'conversions' were forced and the participants had no idea what they were doing. Others alleged that they were lured to the event by the promise of ration cards.

Opposition MPs attacked the BJP government, with the Congress Party leader in the upper house, Anand Sharma, saying: "The House and the country need reassurance that the Constitution will not be violated." A police investigation has begun.