Reuters news agency quoted unconfirmed security sources as saying that three policemen and six Coptic protesters on Wednesday were injured in a clash between the two sides in the southern Egyptian city of Minya.
The agency said the police used batons to beat the protesters, who retaliated against police by throwing stones.
The clashes erupted when the police tried to disperse demonstrators, who blocked a road in protest against the disappearance of two Coptic teenage girls.
The source said the clash took place in front of the Security Directorate, where a thousand Coptic protesters gathered on Tuesday. Hundreds of protesters, who camped out overnight, claimed the girls were abducted by Muslims and forced to convert to Islam.