Cairo - An Egyptian security official says a leading member of the hard-line group Gamaa Islamiya has died in prison.
Interior Ministry official Major General Hassan el-Sohagi said on Sunday that Essam Derbala died of natural causes.
A statement from Gamaa Islamiya's political party accused Egyptian authorities of "assassination”.
It said authorities intentionally deprived Derbala of medicine and subjected him to psychological torture.
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The statement called for responsible officials to be prosecuted.
Derbala was arrested earlier this year and accused of inciting violence.
He was imprisoned in a high-security facility in Cairo called Scorpion.
Gamaa Islamiya waged an armed insurgency in Egypt in the 1990s. The group later renounced violence and was a strong ally of ousted Islamist president Mohammed Morsi before and during his year in office.