The death toll from the car bombing in the Indian capital has risen to 12

India's counter-terrorism unit led its third day of investigations Wednesday into the car bombing in the capital, as a medical official reported that the death toll had risen to 12.

Indian Prime Minister Narendra Modi described the blast, which occurred Monday evening, as a "conspiracy" and vowed to bring those responsible to justice.

Police have yet to provide details about the cause of the massive explosion near the historic Red Fort in Delhi's densely populated Old Delhi district, one of India's most famous landmarks and the site where the prime minister delivers his annual Independence Day address.

The incident was the deadliest since April 22, when 26 civilians, mostly Hindus, were killed at a tourist site in Indian-administered Kashmir, sparking clashes with Pakistan.

"Twelve people have been killed and more than 30 injured," Dr. Ritu Saxena, chief medical officer at New Delhi's LNG Hospital, told AFP.

India’s National Investigation Agency is leading the investigation into the blast, which occurred hours after police announced the arrest of a gang and the seizure of explosives and assault rifles.

Police stated that those arrested have links to Jaish-e-Mohammed, a Pakistan-based group, and Ansar-ul-Ghazwat-ul-Hind, an al-Qaeda affiliate in Kashmir.

India classifies both groups as terrorist organizations.

After chairing security talks following Monday’s explosion, Home Minister Amit Shah said he had instructed officials to “search for everyone involved in this incident.”