CAIRO, Oct 19 (Reuters) - A retrial of former Egyptian President Hosni Mubarak resumed on Saturday in a closed-door session in which top security officials gave testimony, state television said.

Mubarak, 85, was sentenced to life in prison last year for complicity in the killing of demonstrators in the uprising that toppled him in 2011, but an appeals court ordered a retrial.

Mubarak was released from jail but is kept under house arrest in a military hospital in Maadi, a Cairo suburb.

State television said that former intelligence chief Mourad Mowafy and the head of the national security authority, General Mostafa Abdel Naby, testified in Saturday's hearing.

Last month the presiding judge imposed a media gag on the sessions' proceedings for reasons of national security.

The military-backed government imposed a state of emergency after Islamist President Mohamed Mursi was toppled in July, and used this to place Mubarak under house arrest.

The army had removed Mursi, Egypt's first freely elected president, after mass protests against his rule. His now-banned Muslim Brotherhood has described the move as a coup which reversed the gains of the Arab Spring revolution against Mubarak. (Additional reporting by Ali Abdelatti; Reporting by Asma Alsharif; Editing by Yara Bayoumy and Mark Trevelyan)