The bomb blast at a cinema hall in Ludhiana on Sunday night that claimed six lives was of high intensity with the possibility of the use of the deadly RDX was not ruled out, officials said.

The sources said preliminary examination and samples collected from the site gave enough indication that RDX was used to give more charge to the explosive material so that the flying splinters could cover more areas to cause injuries.

They said the crater caused due to the explosion was very deep which indicated that the explosion was of high intensity.

"The impact of the explosion was absorbed mainly by the chairs at the cinema hall as otherwise the casualty could have been more," an official associated with the investigations said.

The sources said RDX could have been mixed with other explosive material with a timer to trigger the blast after 8.30 pm when the bomb planter could have possibly left the cinema hall after the movie interval.

However, a complete picture about the explosive material would be made available only after a thorough examination by the forensic team, the sources said.

The post-mortem of the bodies revealed that some of the six died of heart failure while others succumbed to splinter injuries.