Haryana and neighbouring Punjab have been put on high alert after the incident, official sources said.

The clash broke out after an altercation between two sides during morning prayers - naamcharcha - of Dera supporters in Dabwali town, about 60 km from Sirsa, Deputy Commissioner V Umashankar said.

"One person belonging to the group of Sikh supporters slipped and fell down in the melee and was killed in the brickbatting during the clash. He has been identified as Mandar Singh of Dabwali," Umashankar, who also received minor injury when he went to assess the situation in the town said.

The supporters of each group were carrying weapons, including swords and lathis, during the clash.

After the incident, violence erupted as irate mob went on rampage and damaged about 15 shops in Dabwali and also burnt two of them. Some vehicles were also damaged by the mob.

"Additional forces, including two companies (200 personnel) of Rapid Action Force, have been mobilised from neighbouring districts and have been deployed in Sirsa and Dabwali," Haryana's Additional Director General of Police (law and order) V B Singh said.

He said an FIR had been registered in connection with the incident at Dabwali, which is about 40 km from Punjab's Bathinda district.

The biggest premises of Dera Sacha Sauda is in Bathinda's Salabatpura, a place which has been witness to tension between the Sikhs and Dera followers in the past.

The Deputy Commissioner said that the district administration had not been told about the Dera programme in advance.

"Generally, we are informed about any naamcharcha by the Dera people, but this time we had no information because of which we could not take any action.

"It was a small prayer congregation and not many people from Dera side were present and the Sikh group numbered about 50. There was some altercation between the two groups after which they clashed and also pelted stones at each other," he said.

"We are trying to bring the situation under control. Sec 144 banning assembly of five or more persons has also been imposed in Sirsa. The situation is tense but under control," Umashankar said.

Meanwhile, a group of Sikhs from Punjab has reached Dabwali and protesters have blocked Sirsa-Bathinda road, sources said.

The Dera Sacha Sauda said its followers were holding 'naamcharcha' in the morning peacefully and termed the incident "as an unprovoked one".

"It was a peaceful prayer which was being held by Dera followers. A group of Sikhs armed with weapons and lathis and other firearms attacked the followers without provocation. A group of followers even went to Dabwali police station to demand registration of a case, but police did not act and bundled them inside a bus and took them back to the spot where they were holding naamcharcha. The other group already present there attacked them," the Dera Sacha Sauda's chief spokesman, Aditya Insaan said.

In June, a Sikh was killed in firing by a bodyguard of Dera chief in Mumbai during an altercation with a group of Sikhs, leading to violence.

Insaan alleged that Dera followers holding prayer meeting were accosted but they did not retaliate.

"Our Dera has Hindus, Sikhs and followers from other faiths. We foster Sikh-Hindu brotherhood. We have a humanitarian face and Dera followers have actively participated in blood donation camps and also extended helping hand in earthquakes in J&K and Gujarat in the past," he said.

Insaan alleged that some people with vested interests were trying "portray it as a religious issue".

"Last year Guruji's (Dera chief Gurmeet Ram Rahim Singh) wearing a dress at a congregation was also blown out of proportion by some people with vested interests," he alleged.

The Dera head has been at loggerheads with the Sikhs over the past one year and after the Mumbai incident, several Sikh groups have stepped up their demand for his arrest.

On Friday also, the Sikhs at Dabwali and some other parts upped their demand after the latest incident.

The Dera chief, who also addressed his followers in his Sirsa dera, has been provided Z plus security cover.

Meanwhile, in Punjab a high alert has been sounded and additional forces were being deployed around sensitive places, including Salabatpura in Bathinda, which had in the past witnessed tension between Dera supporters and Sikhs.