CAIRO (AP) — At least 36 people detained on suspicion of taking part in the street clashes roiling Egypt's capital were killed Sunday when security forces fired tear gas inside of the prison truck holding them, security officials said.

Those killed were part of a truck convoy of some 600 detainees heading to Abu Zaabal prison in northern Egypt, the officials told The Associated Press. Detainees in one of the trucks rioted and managed to capture and badly beat up a police officer inside, the officials said.

Security forces fired tear gas into the truck in hopes of freeing the officer, the officials said, adding that those killed died from suffocating on the gas.

The officials spoke on condition of anonymity because they were not authorized to speak to journalists.

However, the officials' reports contradicted state media's version of events. The official web site of Egyptian state television reported that the deaths took place after security forces clashed with militants near the prison and detainees came under fire while trying to escape. The official MENA state news agency also said the trucks came under attack from gunmen.

State media also said all those killed and the gunmen belonged to the Muslim Brotherhood, the organization that ousted President Mohammed Morsi hails from. The officials who spoke to AP said some of the detainees belonged to the Brotherhood, while others didn't.

CAIRO, EGYPT - AUGUST 18: Supporters of deposed Egyptian President Mohammed Morsi. (Credit: Getty Images)

The differences in the accounts could not be immediately reconciled Sunday night.

The officials who spoke to the AP said that the detainees were rounded up during the past two days of street violence around Cairo's Ramses square, clashes that killed scores of people.

Egypt's Muslim Brotherhood group is leading mass rallies against the country's military over the July 3 coup that ousted Morsi. The Brotherhood, long banned in Egypt, rocketed to power in the country's first democratic elections held last year.