"There is a possibility that ammonium nitrate was used," Additional Commissioner of Police K.C. Dwivedi told IANS.

In a July 27 notification, exactly two weeks after the July 13 triple bombings that killed around 25 people in Mumbai, the Indian government listed ammonium nitrate under the Explosives Act, 1884, and banned its open sale, purchase and manufacture.

Deputy Commissioner of Police heading the crime unit Ashok Chand said "shrapnels" were used in the bomb outside the Delhi High Court. This is the third major bombing in India since the 2008 Mumbai terror attacks.

Home Secretary R.K. Singh said the explosion took place around 10.30 a.m. outside Gate No. 5 of the high court complex located close to India Gate in the centre of the capital.