Twelve people were detained on Monday in connection with Sunday's deadly blasts at a Ludhiana multiplex which claimed seven lives.

However, the police are not yet sure about the number of people involved in the blast, Deputy Inspector General (Intelligence) J K Mittal said in Ludhiana on Monday .

He did not rule out the involvement of terrorist outfits, working in Punjab or Jammu and Kashmir [Images], in masterminding the explosion. Punjab Police DGP N P S Aulakh said that the state has been put on high alert in the wake of the blasts.

He refused to rule out the theory that the blast might have been an attempt to scare away migrant labourers, who dominate the labour sector of Punjab.

Meanwhile, four of the six killed in the bomb blast at the Shingar Cinema have been identified as Sonu Sharma, Imtiaz Alam, Vandhan and Shashan Shah. All of them are migrant labourers.

Of the injured, the condition of three victims is reportedly critical.