Indian police were investigating the deadly car explosion in New Delhi under an anti-terrorism law, officials said Tuesday, as forensic experts worked to determine the cause of the blast.

The explosion occurred near the historic Red Fort late Monday, killing at least eight people and injuring several others.

Senior police officials told The Associated Press that a case was registered under the Unlawful Activities (Prevention) Act, India's main anti-terrorism law, which allows broader powers to investigating agencies to detain suspects. The officials spoke on condition of anonymity because of the sensitivity of the case.

Prime Minister Narendra Modi, who was on a scheduled visit to Bhutan on Tuesday, said investigators would "get to the bottom of this conspiracy.

"The conspirators won't be spared and all those responsible will be brought to justice," Modi said.

Police said the explosion was believed to have originated from a Hyundai i20 car that had stopped at a traffic signal. Nearby vehicles were badly damaged, and photos showed shattered windows, twisted metal and flames engulfing several cars.

Police were trying to trace the car's owner. There was no immediate information about the occupants, who were believed to have been killed.

Home Minister Amit Shah said Monday that "all angles" were being investigated and that security agencies would reach a conclusion soon. He said footage from cameras in the area would play a key role in the investigation.

Major train stations, including in Mumbai and in Uttar Pradesh state, which borders New Delhi, were put on security alert. The security force responsible for guarding key installations in the capital, including New Delhi's international airport, metro system and major government buildings, said its personnel had also been placed on security alert.

A former imperial palace, the Red Fort is a sprawling Mughal-era complex and a major tourist attraction in the Old Delhi section of the city. Located about 6 kilometers (3.7 miles) from Parliament, the 17th-century monument is a symbolic location where Indian prime ministers deliver their Independence Day speeches on Aug. 15 each year.

The area around Red Fort is typically crowded, serving as a main route to the bustling bazaars of the old city.

The deadly car explosion in New Delhi is being investigated under an anti-terrorism law