Indian Prime Minister Narendra Modi labeled Tuesday the deadly car explosion that killed at least 12 people in central New Delhi a "conspiracy" and vowed to bring those responsible to justice.
Police are yet to give exact details of what caused Monday's blast near the historic Red Fort, one of India's most well-known landmarks, and the site of the annual prime minister's Independence Day speech.
It is the first significant security incident since April 22, when 26 people were killed at a tourist site of Pahalgam in Indian-ruled Kashmir, triggering clashes with Pakistan.
"I assure everyone that the agencies will get to the bottom of the entire conspiracy," Modi said, in a speech during a state visit to neighboring Bhutan, without giving further details.
"All those involved will be brought to justice."
At least 19 people were also wounded when flames ripped through several vehicles. Crime scene investigators scoured through the wreckage early Tuesday.
The explosion Monday came hours after Indian police said they had arrested a gang and seized explosive materials and assault rifles.
Police said the men were linked with Jaish-e-Mohammed and Ansar Ghazwat-ul-Hind, an offshoot of al-Qaida. Both groups are listed as terrorist organizations in India.
Defense Minister Rajnath Singh, speaking at a conference in New Delhi, said that investigative agencies were "conducting a swift and thorough inquiry" and that the findings "will soon be made public."
Singh, echoing Modi's words, said "those responsible for this tragedy will be brought to justice and will not be spared under any circumstances."
Senior Delhi police officer Raja Banthia said they were investigating the blast in the crowded Old Delhi quarter of the city, under anti-terrorism laws.
New Delhi's deputy chief fire officer, AK Malik, told Agence France-Presse (AFP) shortly after the explosion that eight people had been killed.
The Press Trust of India news agency reported Tuesday that the death toll had risen to 12, although that figure has not been confirmed.
Witnesses described to AFP how the car exploded in traffic and how people caught up in the surge of flames were set on fire.
"I saw the car explode while it was moving," said Dharmindra Dhaga, 27.
"People were on fire and we tried to save them ... Cars and people were burning – people inside the cars were burning," he said.
"I was telling the public to save them, rescue them, and get them out. The public was busy making videos and taking photos."
The emergency ward at Delhi's LNJP hospital was chaotic after the explosion as wounded people streamed in and doctors rushed to treat them.
A woman broke down outside the ward where her husband was being treated.
"I can't bear to see him like that," she said as her brother tried to console her.
