PARIS (Reuters) - An autopsy showed no signs that violence had been inflicted on a young man whose death in police hands sparked two nights of unrest near Paris, a source close to the matter said on Thursday.

The man was suffering from "a very serious infection", the source said. Family members had said earlier that police hit the man as they detained him for trying to prevent the arrest of his brother on suspicion of violence and extortion.

Angry crowds hurled petrol bombs at police and set cars alight in the Val d'Oise region 40 km (25 miles) north of Paris during a second consecutive night of violence following the death of the 24-year old.

Nine people were arrested in the fighting, which involved some 200 locals and 180 police officers, Jean-Simon Merandat, director of the local prefect's office, said.

About 15 cars and dozens of public garbage bins were set on fire by crowds, who also hurled petrol bombs at a nursery school and a town hall, Merandat told public radio station France Info.

Weeks of rioting erupted in Paris's often grim suburbs in 2005 after the death of youths who were electrocuted when they hid from police in a power generation hub.

Merandat told France Info nobody was injured on either side in the second night of confrontation and that calm had returned by the early hours of Thursday.

The protests in the Val d'Oise area began on Tuesday night when, according to deputy prosecutor François Capin-Dulhoste, man died as he was being taken away by police after being arrested.

Five police were slightly injured on the first night, when they were shot at by people with firearms, he said.

Capin-Dulhoste said the dead man suffered a heart problem during transportation to a police station but that the cause of death was being investigated.

(Reporting by Brian Love and Chine Labbe; Editing by Nick Macfie, Larry King)