The probe into the terror attack on the cinema hall in Ludhiana focussed on the suspicion that it could have been a joint effort by Sikh separatists and Islamic militants as 12 persons were detained for questioning.

The terror angle in the terror attack on Shringar multiplex was being pursued with DIG(Intelligence) Jagdish Mittal telling reporters the blast could be a result of a collaboration between the "jihadi groups and the Babbar Khalsa International," a Sikh separatist group. No outfit has so far claimed responsibility.

Punjab's Chief Secretary Ramesh Inder Singh however maintained it was too early to link the blast to any group.

A breakthrough in the blast case is expected in a day or two, said Additional Director General of Police (Law and Order) Chandrashekhar. "It will take a day or two to get the breakthrough."

Investigators were also trying to find out the exact nature of explosives used in the blast, which killed six persons, as a team of National Security Guards and forensic experts examined the site.

Official sources said in Delhi the blast was of "high intensity" and that a preliminary examination of evidence gave enough indication that RDX was used. Police had seized 500 kgs of RDX in Punjab three weeks back.

However, Chandrashekhar said "initial reports do not point to the use of RDX in the blast. Chandrashekhar said the type of burns received by the injured would help in reaching some conclusion about the nature of explosives used the blast.

Another angle being probed is that the blast may be an attempt to scare away migrant workers from Uttar Pradesh and Bihar who dominate the labour sector in Punjab.

Chief Minister Parkash Singh Badal rejected suggestions that the bomb blast after a gap of several years signalled the revival of militancy in the border state.

"People of Punjab have no sympathy with terrorists as they would not allow the hard earned peace to go. There is no chances of revival of terrorism," he said.