Dozens of Egyptian protesters clashed with police outside a Cairo police station on Saturday after a young man died in police custody, state media reported.
Security sources said a young man arrested on Friday for alleged drug trafficking died after a fight with other prisoners. But protesters accused police of being responsible for the man's death.
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The security sources said several people were injured and about 40 people arrested in the overnight clashes in Cairo's Moqattam district.
Some protesters threw petrol bombs as police responded with tear gas and birdshot, and 10 cars were torched, including three police vehicles, they said.
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Cairo's security chief pledged a probe into the detainee's death and promised not to hide any police involvement. The prosecutor ordered an autopsy.
A number of Egyptian police officers have been tried and sentenced over violent deaths in detention in recent years.
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Anger over widespread police brutality contributed to the 2011 uprising that toppled longtime autocrat Hosni Mubarak.
Rights groups have said mistreatment and torture continue to be used widely in Egyptian prisons, but the government has denied this.
Egypt's interior ministry has said it does not condone torture but that there had been "individual" cases of abuses.
In 2013, Egypt banned all unauthorized protests in a widespread crackdown on dissent.
law/rc (AFP, AP)