About 2 kilograms of explosives were used in the blast outside Delhi high court on Wednesday morning which killed at least 11 people and injured over 76 others, the Union home ministry said.
"The explosives quantity is estimated to be about 2 kilograms which created a crater two feet wide and one feet deep. It is deduced that most of the casualties have been caused by the blasts (not by shrapnels)," Secretary (Internal Security) in MHA, U K Bansal told mediapersons.
He said that preliminary forensic investigations reveal that explosives used could be nitrate-based.
"Some traces of PTN are also being suspected," Bansal said. PTN, short for pentaerythritol trinitrate, is a chemical explosive that has a long history of terrorist use.
The official said that the National Investigating Agency has taken up the investigation and has deployed a team of 20 officers to go into various aspects of the probe.
Bansal said that detailed forensic examination is going on and investigators were trying to ascertain the authenticity of an email sent to certain media houses purportedly by Harkat-ul-Jehadi-Islami, a banned terror group, claiming responsibility for the blast.
NIA has also sought Delhi police's help in the investigations.
Bansal said Prime Minister Manmohan Singh has announced an ex gratia of Rs 2 lakh for the next of kin of those killed in the blast and Rs 1 lakh to the injured.