Egyptian soldiers beat and tortured protesters they had arrested at a demonstration near the Defence Ministry this month, Human Rights Watch (HRW) said on Saturday, citing victims and lawyers.
The New York-based group said soldiers arrested at least 350 protesters, including 10 children and 16 women, on May 4 amid violence over a sit-in begun a week earlier in protest at the exclusion from Egypt's presidential race of Hazem Abu Ismail.
Military prosecutors ordered them detained pending trial in military courts and at least 256 are still held, HRW said, adding many of those released told of torture and beatings.
"The brutal beating of both men and women protesters shows that military officers have no sense of limits on what they can do," said Joe Stork, HRW's deputy Middle East and North Africa director.
The group also said the military had failed to protect protesters from attacks by unidentified armed groups on May 2 in central Cairo's Abbasiya district near the Defence Ministry.
Up to 11 people were killed in that day's violence. One soldier was killed and almost 400 people were wounded in the clashes on May 4. The streets have been mostly calm since then.
Egyptian officials made no immediate comment on HRW's statement.
The country holds its first genuinely contested presidential election next week to replace Hosni Mubarak, deposed in February 2011 by a popular uprising. A run-off vote is likely in June.
A military council is overseeing a turbulent transition and has promised to hand over to the new president by July 1.
HRW said there had been no accountability for earlier cases of torture by the military documented by itself and Egyptian human rights groups over the past year of army rule.
"Egyptians won't feel secure until there is a law enforcement system they can trust to police demonstrations effectively and protect them from attacks by thugs," Stork said.
(Writing by Alistair Lyon; Editing by Sophie Hares)