LONDON: More than 50 prisoners are still missing since riots at Syria`s Saydnaya prison two years ago led to the deaths of at least 17 prisoners and five military police, Amnesty International said on Monday.

In a report marking the second anniversary of the July 5, 2008 riots at the prison north of Damascus, Amnesty said it was stepping up a campaign "to uncover the truth about all of Saydnaya’s missing prisoners."

The London-based group said at least 52 detainees have gone missing since the riots and that "18 of the prisoners are victims of enforced disappearance, as defined by international law."

Two of those 18 prisoners, human rights defender Nizar Ristnawi and Basel Madarati, had completed their prison terms respectively on April 18, 2009 and January 20 of this year, but were not freed, Amnesty said.

Their families and lawyers had been denied access to them and their fate is unknown, it added.

"At the time of writing, the Syrian authorities, while acknowledging or implying that they were holding all of the (18) men apart from Nizar Ristnawi, were still refusing to provide any other information about their fate or whereabouts," Amnesty said.

Madarati`s father told Amnesty that "prisoners released from Saydnaya prison have told him that his son was killed in the disturbances and that his body has been stored in a freezer since 25 November, 2008, but he has been unable to verify this," the report said.

Calling the Saydnaya prison "Syria`s Black Hole," the report said prisoners held there "have extremely limited access to the outside world.

"Their lawyers are never allowed to visit them, and their families are allowed at most one visit a month after obtaining a permit" that is difficult to secure.

Syrian rights groups say that more than 25 inmates were killed in the rioting two years ago that lasted for at least two days.

Syria stopped prison visits for a year following the riots.

The Syrian authorities have blamed inmates for provoking the riots, for which a casualty toll was never released.

"Prisoners sentenced for crimes of terrorism and extremism caused trouble ... in Saydnaya prison. They attacked their comrades during a prison inspection," an official statement said at the time.

But the London-based Syrian Observatory for Human Rights, which is close to the opposition, said more inmates were killed when military police fired live rounds at Islamist prisoners who rioted after a raid by guards.

Saydnaya jail was built in 1987 to accommodate 5,000 inmates, but it has since been used to house up to 10,000, according to Syrian rights groups.

BDST: 09:12 HRS, July 5, 2010