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Here's what to know about the explosion:

A car blew up while waiting at a red light

The explosion occurred just before 7 p.m. local time on Tuesday evening and is believed to have originated from a Hyundai i20 car that had stopped at a traffic signal, Home Minister Amit Shah said. The blast triggered a fire that engulfed several nearby cars and rickshaws.

“A slow-moving vehicle stopped at a red light. An explosion happened in that vehicle, and due to the explosion, nearby vehicles were also damaged,� Delhi Police Commissioner Satish Golcha said.

Photos from the scene showed shattered windows, twisted metal and flames consuming vehicles. The blast left mangled bodies and wrecked cars scattered near the site as police and investigators cordoned off the area and pushed back growing crowds.

Om Prakash Gupta, who lives nearby, told The Associated Press he heard the explosion while in his house: “I rushed out with my children and saw several vehicles on fire, body parts all over."

Authorities said the injured were being treated at a nearby government hospital.

The cause of the explosion is not clear

An investigation into the cause of the explosion is underway. The ºÃÉ«tv Investigation Agency, India’s federal anti-terrorism body, along with forensic experts, is leading the probe.

Home Minister Shah, who visited the site, said “all angles� were being investigated and that security agencies would reach a conclusion soon. He said footage from cameras in the area would form a key part of the investigation.

“We are exploring all possibilities and will conduct a thorough investigation,� Shah said.

Key facilities placed on security alert

Authorities placed major train stations across India, including in Mumbai city and in the northern state of Uttar Pradesh, which borders New Delhi, on security alert following the explosion, officials said.

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.

The U.S. Embassy in New Delhi urged its citizens to avoid crowds near the Red Fort and stay alert in tourist areas.

Red Fort is a popular tourist destination

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 six kilometers (3.7 miles) from Parliament, the 17th-century monument is a where Indian prime ministers deliver their annual Independence Day speeches on Aug. 15.

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