Terror revisited New Delhi on Wednesday when a powerful explosion ripped through a crowd at the Delhi High Court, killing 11 people and injuring at least 76 in India's third worst bombing since the November 2008 Mumbai attack.

The suitcase bomb went off around 10.30 a.m. just outside Gate No. 5 of the complex near India Gate in central Delhi where passes are issued for the hundreds of litigants, media personnel and other visitors to the court.

Around 300 people were waiting outside various gates of the court when the blast took place.

According to Home Secretary R.K. Singh, the bomb was in a suitcase. "We have remains of the suitcase," he told reporters.

Police also suspect the use of ammonium nitrate in the explosive.

"We are investigating how the brief case was placed there It is not a controlled area. There were lots of people," said Special Commissioner Dharmendra Kumar.

Terror email

And in an email to various media houses Pakistan-based Harkat-ul-Jehadi Islami has claimed responsibility for bombing outside the Delhi High Court.

In an email sent from an unknown location to various media houses, HuJI demanded the death sentence of 2001 parliament attack convict Afzal Guru be immediately 'repealed'.

"We own the responsibility of today's blast at (the) high court (in) Delhi. Our demand is that Afzal Guru's death sentence should be repealed immediately else would target major high courts and the Supreme Court of India," the email read.

Guru has been sentenced to death by the Supreme Court after he was convicted for the December 13, 2001 parliament attack.

"We are taking the email seriously," National Investigation Agency (NIA) chief S.C. Sinha told reporters.

'Unite to crush terrorism'

Prime Minister Manmohan Singh in a statement condemned the blast saying the country 'must unite to crush the scourge of terror'

"This is a long war in which all political parties, all the people of India have to stand united so that the scourge of terrorism is crushed," Singh said from Dhaka, where he is on a trade visit.

Scenes of horror

At the site, where the blast was marked by a crater, Bhagwan Das, an eyewitness, recounted his 'close encounter' with a moment of terror that left him numbed.

"I saw some people losing their hands and legs. Their bodies drenched in blood. God, it was terrible," Das said.

At the nearby Ram Manohar Lohia Hospital where the injured were taken, the scene was grim.

Allauddin, 40, lost one of his legs in the blast. He was at the court for the hearing of a case related to his factory.

"My son...my son lost his leg," cried his devastated father, as scores of people scurried around him.

There was intelligence

Home Minister P. Chidambaram admitted in the Lok Sabha that Delhi Police did receive intelligence inputs on terror threats in July this year. He also said the attack occurred although the capital was on high alert.

"Intelligence pertaining to threats emanating from certain groups was shared with Delhi Police in July… despite Delhi Police remaining on high alert, the tragic incident occurred today," he said.

The minister said the investigation will be handed over to the National Investigation Agency (NIA).

The terror attack on Wednesday is also the second time in four months that the Delhi High Court has been targeted. On May 25, a low-intensity explosion, from a plastic bag near a car, took place without causing any damage.