Hundreds of protesters pelted the security headquarters in the Egyptian city of Suez with rocks on Wednesday, angered by a court's decision to uphold the release of seven policemen facing trials for allegedly killing protesters during the country's uprising.

Riots and protests have been escalating recently over what many see as the reluctance of the military rulers to prosecute police and former regime officials for the killing of nearly 900 protesters.

Ahmed el-Ganadi, the father of a protester killed in Suez during the revolt, said hundreds of residents had marched towards the government building housing the courts and security headquarters to protest against the court decision.

"The courts are corrupt. They are complicit in denying us justice," Ganadi said. "We will no longer wait for a court decision to get our retribution."

Suez, at the southern tip of the strategic Suez canal, was the scene of some of the most dramatic confrontations between police and protesters during the 18-day uprising that ousted President Hosni Mubarak in February.

The military council that took over from Mubarak has promised democratic elections in the coming months and a transition to a civil government.

Justice for those who killed demonstrators has become a rallying point for the protest movement, which has splintered in political debates over how to manage the transition period.

"This is the spark … God help us with what is to come," Ganadi said.

The court in Suez rejected an appeal against the decision in a Cairo court on Monday to grant bail to seven policemen facing trial for the killings of 17 protesters in Suez.

The angry relatives stormed the Cairo courtroom after the initial ruling on Monday, while others blocked a highway linking Cairo to Suez for hours. Hundreds in Suez have been holding a sit-in since Monday at one of the city's main squares.

Lawyers said the courts had consistently denied a request to add more policemen to the case.

"A sit-in until we get retribution," read one of the signs raised by the protesters.

There are already calls for large protests in Egypt this week demanding fair trials and retribution, as well as measures to purge former regime officials from political and economic life.

Only one policeman has been convicted in more than a dozen court cases over the deaths of at least 846 people killed in the government crackdown on protesters. He was tried in absentia.

Mubarak and his two sons also face charges of killing protesters and amassing illegal wealth. Their trial is scheduled to begin on 3 August.

Protesters complain that court officials have generally been lax with police officers accused of shootings during the uprising, allowing many to stay in work while facing murder charges or setting them free on bail. They say this leaves victims' families subject to intimidation.

By contrast, human rights activists complain that minor offenders and protesters are referred to military tribunals known for quick and harsh sentences.