A powerful bomb exploded outside the High Court building in the Indian capital Wednesday, killing at least 11 people and injuring some 76 others.

Police say the “medium intensity bomb” was hidden in a briefcase near a main gate to the courthouse in New Delhi, where people were waiting to enter the building.

Authorities say they are investigating an emailed claim of responsibility by Harkat-ul-Jihad al-Islami, an al-Qaida-linked militant group active in the region.

The email warned that other courts in the country would be attacked unless India repealed the death sentence given to a man convicted in connection with the 2001 attack on India's parliament.

Indian Prime Minister Manmohan Singh, who is on a visit to Bangladesh, condemned the bombing as “cowardly” and urged Indians to stand together so that the “scourge of terrorism is crushed.” Pakistan President Asif Ali Zardari and Prime Minister Yousuf Raza Gilani also condemned the attack and expressed hope that the perpetrators will be brought to justice.

A United Nations spokesman said Secretary-General Ban Ki-moon expressed his solidarity with the government and people of India, saying there is no justification for indiscriminate violence against civilians.

U.S. State Department spokeswoman Victoria Nuland also condemned the bombing, saying United States stands with India in confronting the global challenge of terrorism.

Similar condemnations were issued by the leaders of Britain and France.

Wednesday's blast is the first major terror attack in India since near-simultaneous triple bomb blasts targeted India's financial capital, Mumbai, in July, killing some 20 people. No one has been arrested in that case, but authorities say they have focused their investigation on the domestic Indian Mujahideen militant group.

It also is the second explosion at the High Court this year. In May, a small bomb exploded outside the same court, but did not cause any casualties.