Indian police detained for questioning three people Thursday, including the owner of an Internet cafe in Kashmir, over an e-mail allegedly claiming responsibility for the deadly bombing at the New Delhi High Court, police said.

A powerful bomb, weighing 2 kg and hidden in a briefcase outside the main entrance of the High Court, killed 12 people on Wednesday.

Senior police officers told Reuters that they had detained the owner of an Internet cafe in the Kishtwar region in southern Indian Kashmir, where they suspect the e-mail was sent early Wednesday.

Indian authorities are investigating the claim of responsibility allegedly made in the email by the Harkat-ul-Jihad Islami Muslim extremist group, an al-Qaida affiliate with bases in Pakistan and Bangladesh. It has claimed responsibility for attacks in India in the past.

The e-mail to the National Investigation Agency demanded that India rescind the death sentence of a man convicted for an attack on the Indian parliament in 2001 and warned it would otherwise target major courts in the country.

Security sources in Indian Kashmir, who declined to be identified, have raised doubts about whether HUJI was behind the blast, saying the group had not been active in the region for some time and would not have used an Internet cafe to send a claim of responsibility.

Several Islamist groups have been fighting against Indian rule of the disputed region of Kashmir for years.

Ilyas Kashmiri, who U.S. authorities believe was recently killed in Pakistan, was the head of HUJI and senior al-Qaida member.

The Indian government was sharply criticized for failing to put in place sufficient security measures at such a high-profile location as the High Court, especially as the blast came only days ahead of the 10th anniversary of the Sept. 11, 2001 attacks in the United States.

The High Court was also bombed in May, but no one was injured.

There were no surveillance cameras at the court and hand-held security scanners were not working, lawyers working there said.

(Reporting by Sheikh Mushtaq; Writing by Paul de Bendern; Editing by Yoko Nishikawa)