SRINAGAR, India (Reuters) - Indian police detained three people for questioning on Thursday, including the owner of an Internet cafe, over an email allegedly claiming responsibility for a bombing that killed 12 people in New Delhi, senior police sources in Kashmir told Reuters.

The owner, his brother and an employee of the Global Cyber Cafe in Kishtwar, a city in the Indian administered state of Jammu and Kashmir, were taken in for questioning over an email allegedly linked to a powerful bomb that exploded at the entrance of the High Court on Wednesday.

The authorities are probing the authenticity of an email claiming to be from the militant group Harkat-ul-Jihad Islami (HUJI) and sent from the Internet cafe.

The militant group, affiliated with al Qaeda and largely based in Pakistan but also with bases in Bangladesh, has claimed responsibility for attacks in India, but not in recent years.

New Delhi and Islamabad are just rebuilding ties after peace talks were broken off following the attacks on Mumbai in 2008 when Pakistani militants rampaged through the city, leaving 166 dead. Any possible links between Wednesday's blast and Pakistan could burden the fragile process.

The government has been sharply criticized for failing to put in place sufficient security measures at such a high-profile location as the High Court of the Indian capital, especially as the blast came only days before the anniversary of the September 11, 2001 attacks in the United States.

Prime Minister Manmohan Singh conceded on Wednesday militants were exploiting weaknesses in India's security apparatus.

Security sources in Indian Kashmir, who declined to be identified, have raised doubts about whether HUJI was behind the bomb, 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 a senior al Qaeda member.

Indians woke up to pictures of mangled and bloodied bodies on the front pages of newspapers on Thursday. The public mood against the government, already soured by months of anti-corruption protests, again worsened as crowds jeered ruling Congress party members attempting to meet the victims.

Police released sketches of two men with short beards who were suspects in the attack. Local reports also said on Thursday that the getaway vehicle had been located in a satellite town in the neighboring state of Haryana, but a Delhi police spokesman denied it was linked to the blast.

The High Court was also bombed in May, but caused no injuries.

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

In an email to the National Investigation Agency (NIA), allegedly from the South Asian militant group, it called on India to repeal the death sentence of a man convicted in connection with an attack on the Indian parliament in 2001 and warned it would otherwise target major courts in the country.

The house of another suspected member of HUJI, linked to an attack of the city of Varanasi five years ago, was raided on Wednesday, though local police said the raid was unrelated to the Delhi court blast.

(Writing by Paul de Bendern; additional reporting by Alka Pande in Lucknow and Annie Banerji and Matthias Williams in New Delhi; Editing by Yoko Nishikawa)

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