Hundreds of Egyptians scuffled with security guards in a court in Cairo and blocked a major road for hours after a judge ordered the release of 10 police officers charged with killing protesters during the country's uprising.

Monday's unrest added to tensions already running high in Egypt over the ruling military council's failure to hold accountable security forces involved in killing protesters during the demonstrations that toppled the former president, Hosni Mubarak.

Nearly five months later, only one police officer has been convicted in the deaths of more than 846 people killed in a government crackdown on protesters. He was tried in absentia.

During court proceedings on Monday, guards had to intervene to separate relatives of the victims and families of the defendants, even before the decision was read. In his initial statement, the judge seemed to suggest he would impose harsh sentences, saying that "the blood of those killed will not be spilled in vain", according to the Egyptian news agency Mena.

However, he then ordered the release of the defendants, sparking a riot. The victims' families scuffled with the guards and tried to rush toward the defendants, who were hurried out of court. A number of relatives of the protesters killed in the uprising tried to storm the judge's office, but were blocked by soldiers.

Egypt's prosecutor-general, Mahmoud Abdel-Meguid, ordered the court's decision overturned in an attempt to defuse anger. But a lawyer for the victims' families said the move was "illegal" because the prosecutor-general had no authority over the court. "They are trying to deceive the people to pacify them," said Amin Ramez, a lawyer. "The policemen are now at army headquarters seeking protection. If people saw them, they would tear them apart."

Ali el-Ganadi, father of one of the victims, said he received a promise from the prosecutor-general to enforce the annulment of the court's order and bring the officers back to jail.

Relatives of those killed in the uprising blocked traffic for at least six hours on the road from Cairo to Suez, leaving hundreds of cars lined up. The court case involved protesters killed in Suez.

Ramez spoke to Associated Press by phone from the Cairo-Suez road, about 60 miles outside of Cairo. He said truck drivers and Suez residents joined the protesters while the military tried to negotiate the blockade.

A couple of hours after nightfall, El-Ganadi, the spokesman for Suez victims' families, said the protesters had started reopening the road. After clearing the street, they moved to Suez, according to one protester, Ahmed Khafagi. He said traffic has been halted inside two main squares in the city and thousands of people are rallying and chanting slogans, including "Down with the military junta". "People are boiling," an activist, Ahmed Abdel Gawad, said.

The policemen were charged with killing 17 people and injuring more than 350 in Suez during the 18-day uprising that ended with the ousting of Mubarak on 11 February. The court released seven of them on bail and postponed their trials until 14 September. Three are being tried in absentia.

Suez was a flashpoint of violence during the uprising, with many deadly confrontations between tens of thousands of protesters and security forces. Footage posted on YouTube showed police officers at a police station in the main square opening fire on protesters.

Ramez said the court over the past four sessions had rejected demands by families' lawyers to add 41 other police officers to the case. "We provided them with footage and visual evidence that show those policemen holding guns and automatic weapons and hunting down the protesters as if they were hunting birds. But the judge didn't summon them."The spark of the revolution came from Suez and the second revolution will also come out of Suez," he said.

The release of the officers has strengthened plans for a million-strong rally on 8 July to push for fair trials of former regime members, including senior security personnel suspected of giving the order to shoot protesters during the uprising.

Mahmoud Ibrahim, one of the youth groups that led the uprising, said Suez residents were planning to turn out in force for the demonstration.

In Cairo, a security official said anti-riot police fired teargas to disperse dozens of people around a police station in the centre of the city. The reason for the tensions there could not immediately be confirmed, he added.

Suez is located at the southern end of the Suez Canal, which links the Red Sea and the Mediterranean. The waterway is a vital source of foreign currency.