A man detained in an Alexandrian police station died on Saturday while in custody, reported Al-Ahram Arabic website.
The 58-year-old man was arrested during an opposition protest on Friday and according to police sources is a supporter of the Muslim Brotherhood, Al-Ahram reported.
Several prisoners have died in police custody over the past year amid allegations of police negligence, ill-treatment, or torture.
An Alexandrian police source denied that the victim, Mahmoud Hanafy, had died because of negligence.
He told Al-Ahram that Hanafy's medications were offered to him and an ambulance rushed to the station as soon as it was reported that he lost consciousness.
Hanafy had not yet been referred to the prosecution.