Home minister P Chidambaram has indicated that the blast in the Delhi High Court could have been carried out by home grown militants groups. "We can no longer point to cross-border terrorism as a source of terror attacks in India," Chidambaram told the BBC in an interview.
He said the authorities were still trying to verify emails allegedly sent by two groups claiming responsibility for Wednesday's attack.
The two groups who have purportedly said they carried out the attack are Harkat-ul Jihad al-Islami (HuJI), which has Pakistani origins and is accused of links to al Qaeda, and the Indian Mujahideen.
The home minister said even though HuJI had claimed responsibility for the blast, the group had not been active in India for a while.
"There have been three major attacks in India recently -in Pune, Mumbai (Bombay) and Delhi. In respect of the Mumbai and Pune attacks, we are fairly certain they were carried out by Indian modules or India-based modules," he said.
In the past, India has often blamed Pakistan-based groups for carrying out attacks on its soil.
"That threat remains - but we must also look at Indian modules or India-based modules which are capable of carrying out terror attacks," he said.
Chidambaram said the country's proximity to Pakistan and Afghanistan was a cause for worry and India was concerned about how to prevent the "radicalisation" of its youth.
"The government can build capacity and extend the intelligence network, but policing is a very complex task and there will be cases where the terrorist is able to slip through the cracks," he said.