Egyptian protesters clashed with soldiers and police in Cairo on Friday after a funeral procession for a man a rights group claims died from police torture after he was caught smuggling a mobile phone chip into his cell.
Dozens of protesters hurled stones at soldiers and police after relatives of Essam Atta brought his coffined body to Tahrir Square, where thousands were rallying to demand the military cede power to a civilian government.
The protesters, who had branched off from the rally to join the procession, chanted "the people demand the execution of the field marshal," referring to the country's military ruler, Hussein Tantawi.
Soldiers and policemen fired a few warning shots in the air as the protesters pelted them with stones.
Other protesters eventually persuaded the stone-throwers to back off.
One was dragged away by his comrades flailing and screaming: "They have killed another of my countrymen! Screw the military!"
Atta's family had brought his body from a morgue where it had undergone a quick autopsy, witnesses said.
The Nadeem Centre for the Rehabilitation of Victims of Violence said on its Facebook page on Thursday that Atta died after policemen pumped water through hoses inserted in his mouth and anus, a claim denied by a security official.
Atta "was subjected to savage torture; water hoses were inserted into his mouth and anus, and he was then transferred without his parents knowledge to (a Cairo hospital) where he died," the group said.
It said he was tortured after he smuggled the phone chip into prison.
The interior ministry said Atta, who was convicted by a military court for "thuggery and illegally occupying an apartment," died on Thursday as a "result of an unknown poison."
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A prison doctor who examined him found that Atta was suffering from "an apparent severe drug poisoning," the statement on the ministry's website said.
It said he fell unconscious, foamed at the mouth and died on the way to hospital.
A security official, speaking on condition of anonymity, said Atta died after swallowing a bag of pills.
Aida Seif al-Dawla, the Nadeem Centre's director, said Atta's fellow inmates told his brother that he was tortured with the water hoses.
She said the autopsy, which she attended, was superficial and the morgue was not equipped for forensic examinations.
"There has to be an impartial investigation, a professional forensic investigation," she told AFP.
Grainy footage of Atta's corpse in a morgue, posted on YouTube, shows blood and foam on his bandaged face.
Although the cause of his death is disputed, the graphic footage of Atta's corpse and the police's explanation for his death are reminiscent of another young man's death that helped spark the revolt that toppled president Hosni Mubarak in February.
The uprising was inspired in part by calls from activists on a Facebook page set up to protest that death of another young man, Khaled Said, after a beating by police.
"I see a lot of similarities," Seif al-Dawla said.
At the time, police said Said died after choking on a bag of drugs, but pictures of his corpse showed a badly mangled face with a wrenched jaw and a missing lip.
On Wednesday, the Alexandria Criminal Court sentenced two policemen to seven years in jail with hard labour in the case of Khaled Said's death.
Rights groups say torture was routine under Mubarak's 30-year rule. The military, which took over after his ouster, has also been accused of torturing detainees, a charge it denies.