"I do not think anyone can accuse this government of not doing enough," P. Chidambaram told reporters two days after a bomb ripped through a crowd outside New Delhi's High Court, killing 13 people.

The government – and Chidambaram in particular – has borne the brunt of public anger over India's apparent inability to prevent bombings in its cities, despite an overhaul of domestic security following the 2008 Mumbai attacks.

A day after the Delhi court blast, the front page of one national newspaper carried a large photo of the home minister under the one-word headline: "Clueless".

Chidambaram argued that India's sheer size, coupled with decades of "accumulated neglect" of internal security, meant that building sufficient counter-terror capacity would inevitably take time.

"What we can do and will do... is to build capacity brick by brick so that we are in a position to prevent... and neutralise a terror attack.

"There is not a day that passes that we are not adding a brick to our security system and to our security architecture," he said.

Experts say Indian security agencies, and in particular the police, suffer from under-funding, a lack of training and poor intelligence gathering.

Briefing reporters on the investigation into Wednesday's attack, Chidambaram said that police in Indian Kashmir had detained a man suspected of sending an email claiming responsibility for the court bombing.

The unverified email, which said the Pakistan-based militant group Harkat-ul-Jihad al-Islami (HuJI) was behind the blast, had been traced to a cyber cafe in Kishtwar, near the Kashmiri city of Jammu.

"The person we were looking for -- the suspect who sent the e-mail -- has been located and taken into custody for questioning," Home Minister P. Chidambaram told reporters in New Delhi.

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.

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.

Wednesday's bombing 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.