Story highlights Four of the driver's family members are being held by police

Five attacks in four months on security forces in Paris

Paris (CNN) Tourists strolling along Paris' famous Champs-Elysees on Monday afternoon watched in horror as a car rammed into a police van -- and some witnessed the car burst into flames as police grabbed the man inside and put him on the ground.

The armed driver deliberately plowed into the police vehicle and later died, authorities said.

"We were waiting to cross the street and suddenly heard an explosion and the car was in flames," said Eugenio Morcilla, who captured video after the collision. "The police acted very quickly."

Early Tuesday, the Paris prosecutor's office confirmed four of the driver's family members were being held by police.

@rtve el momento después de la explosión del coche en #ChampsElysees, forcejean con el sospechoso para sacarlo pic.twitter.com/o4km0SByTJ — Eugenio Morcillo (@elugeescojonudo) June 19, 2017

It's the latest in a series of terror attacks this year against security forces in the French capital. The Paris prosecutor's office has opened an anti-terror investigation.

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