The National Investigation Agency (NIA) was on Thursday handed over the probe of the bomb blast outside the Delhi high court which has killed nine people and injured nearly 50 people and a special team of 20 members was formed to investigate the terror strike.

A notification was issued by the union home ministry this afternoon handing over the probe to the NIA. This is the first case handed over directly to probe agency formed in the aftermath of 2008 Mumbai terror attacks.

Briefing reporters, director general of NIA S C Sinha said a special investigation team headed by deputy inspector general Mukesh Kumar with superintendent of police Nitish Kumar as chief investigating officer has been set up.

The team will have one more SP and two Additional SPs and two DySPs and the total strength will be 20, he said.

Asked about the mail received by a TV channel purportedly written by Harkat-ul-Jehadi Islami, Sinha said "it is too premature to comment on HuJI mail but we are looking at it seriously because HuJI is a very prominent terrorist group which considers India as target number one."

He said there were no clear leads as of now but "we are working on several theories on several aspects. Some tests have been done on the spot which have been inconclusive...some more tests have to be done in the laboratory and that will tell the details.

"I think we will be able to know shortly the kind of explosives used in the blast," he said.

The mail received by a TV channel claimed that the blast was carried out by HuJI to demand revocation of death sentence of Afzal Guru, a condemned prisoner in Parliament attack, and also threatened to carry out such attacks at Supreme Court if their demands were not met.