Speaking in parliament, he said the government condemned "this terrorist act". He said Delhi was a "target of terrorist groups".

Police said the bomb was apparently placed in a case outside the main gates leading to the reception at the court.

Police have now placed Delhi and the financial capital Mumbai on a state of high alert.

It was caused by "at least a medium-intensity bomb", home ministry official UK Bansal said.

"It appears that the bomb was in a suitcase because we have the remains of that suitcase," the senior civil servant in the home ministry, RK Singh, said.

Intelligence pertaining to threats emanating from groups was shared with Delhi police in July, Mr Chidambarm said. It was not possible to identify the group which caused the blast, he added.