The United States describes HuJI as a terrorist group with links to al Qaeda, and it has been accused of carrying out attacks in India, Pakistan and Bangladesh. - Reuters (File Photo)

SRINAGAR, India: Police in Indian Kashmir said Friday they had detained five people as they investigate an email claiming responsibility for a bomb at New Delhi's High Court that left 13 dead.

The email, purportedly sent by the Pakistan-based militant group Harkat-ul-Jihad al-Islami (HuJI) following the bombing on Wednesday, was initially traced to a cybercafe in a town near the Kashmiri city of Jammu.

After detaining two brothers who owned the cafe and an employee on Thursday for questioning, a police official said two college students - identified as being in the cafe when the email was sent - had also been taken into custody.

“The owners have told interrogators that they don't keep a record of the visitors and that students were the main customers at the cafe,” the official said.

The United States describes HuJI as a terrorist group with links to al Qaeda, and it has been accused of carrying out attacks in India, Pakistan and Bangladesh.

But the group has not been active in Muslim-majority Kashmir for years.

Federal investigators have yet to confirm whether the email was indeed from HuJI.

Another claim of responsibility, apparently from a home-grown militant outfit called Indian Mujahideen, was sent to media on Thursday.

Wednesday's powerful blast ripped through a crowd of litigants queuing to enter the court complex in the heart of the Indian capital.

Eleven people were killed on the spot, and two have since died in hospital from their injuries.

It was the first major attack on Indian soil since triple blasts in Mumbai on July 13 killed 26 people. It has still not been established who carried out those bombings.

The Delhi High Court had been targeted four months ago, when a low-intensity bomb exploded in the parking lot, causing no casualties and only minimal damage.

The probe into Wednesday's bombing is being run by the National Investigation Agency (NIA), a body set up in the wake of the 2008 Mumbai attacks by Islamist gunmen that left 166 people dead.