Groups of men armed with knives and sticks have attacked protesters trying to march to the headquarters of Egypt's military rulers, setting off fierce street clashes.
The clashes come as tensions have been rising between the military council which took control of the country after a popular uprising forced ex-president Hosni Mubarak and activists who want them to move faster in bringing former regime officials to justice and setting a date for the transition to civilian rule.
A crowd estimated at around 10,000 people set out from Tahrir Square in the capital, Cairo, but was stopped from reaching the military headquarters in the eastern Abbasiyah neighbourhood by a line of army barricades. On the way, they chanted slogans against the military council's delay in implementing their demands.
Bands of men armed with knives and sticks set upon them from side roads, triggering pitched street battles in which both sides threw punches and hurled rocks. Gunfire was heard, but it was unclear who was shooting.
It was not clear who the attackers were. Similar groups of men have tried to break up other protest rallies, and Mr Mubarak's regime often used hired thugs to attack protesters. Some witnesses said they might have been residents or shopkeepers angry at the loss of business as a result of the protests.
Hours before the march, the head of the ruling military council praised the youth who led the uprising which toppled Mr Mubarak in an apparent effort to defuse the growing hostilities between activists and the army.
Many protesters have grown distrustful of the military rulers who assumed control of the country on February 11. Critics accuse the generals of dragging their feet in bringing former regime officials to trial and purging the government of Mubarak loyalists as well as trying civilians in military courts.
The march was the second consecutive day that protesters had tried to reach the headquarters of the Supreme Council of the Armed Forces. On Friday, crowds tried to reach the building to denounce the purported beatings of demonstrators by military forces during another rally in the city of Alexandria.
The army quickly issued a statement denying the use of violence against protesters and accusing activists of trying to divide the country. "The Supreme Council of the Armed Forces urges the public to exercise caution and not to be drawn into this suspicious plot that aims to undermine Egypt's stability," the statement said.
The head of the council, Field Marshal Mohammed Hussein Tantawi, tried to soften the tone in an address on state TV on Saturday. He called the youth activists "a great product of Egyptian soil, who belong to an ancient people, adopted noble principles, confirmed their nationalistic sense and realised their responsibility as Egypt's youth to progress and make history". He also appealed for national unity.