New Delhi

India's leading probe agencies are conducting a swift and thorough inquiry into the Delhi blast and those responsible for the tragedy will not be spared, Defence Minister Rajnath Singh said on Tuesday.

Twelve people were killed in the blast that took place in a slow-moving car at a traffic signal near the Red Fort metro station on Monday evening.There is no official word yet on what caused the blast.

"I wish to assure my fellow citizens that the country's leading investigative agencies are conducting a swift and thorough inquiry into the incident," Singh said at a defence conclave.

"The findings of the investigation will soon be made public. I want to firmly assure the nation that those responsible for this tragedy will be brought to justice and will not be spared under any circumstances," he said.

The defence minister also extended his condolences to the families of the deceased.

"I extend my heartfelt condolences to all those who lost their lives in the tragic accident. I pray to God to grant strength and solace to the bereaved families in this hour of deep grief," he said.

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The Delhi Police on Monday night said nine people were killed in the blast and several others sustained injuries. The death toll has gone up to 12 with three people succumbing to their injuries, it said on Tuesday.