A powerful bomb exploded outside the High Court building in the Indian capital Wednesday, killing at least 11 people and injuring some 66 others.

Police say they believe 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.

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.”

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The email warned that other courts in the country would be attacked unless India repealed the death sentence given to a man convicted in connection with the 2001 attack on India's parliament.

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.