Two days of street battles between security forces and protesters in Cairo show just how volatile Egypt remains nearly five months after the popular uprising that ousted authoritarian leader Hosni Mubarak.

More than 1,000 people were hurt in the unrest on Tuesday and yesterday, driven by discontent over the slow pace of justice for old regime figures accused of corruption and killing protesters.

The clashes in Tahrir Square - the worst since the 18-day uprising - add a new layer to an already painful and chaotic transition from Mr Mubarak's regime to democratic rule under the supervision of the military.

The violence will likely set back efforts to empower the discredited police to fully take back the city's crime-ridden streets after they melted away during the early days of the January 25 to February 11 uprising.

Additionally, it will almost certainly deepen the distrust felt by many Egyptians toward the 500,000-strong security forces blamed for the worst human rights abuses during Mr Mubarak's 29-year rule.

Gigi Ibrahim, one of the protesters, said security forces rained tear gas on demonstrators this week.

"It was like January 25 again," she said. "The protesters have enough anger, either because change has not come or because the Supreme Council of the Armed Forces hasn't done enough" to meet their demands.

In Washington, US State Department spokesman Mark Toner said the latest unrest "underscores the fact that this is a very difficult period for Egypt.

"It's a period of transition and we remain committed to assisting the people of Egypt as they make their way through this period of democratic transition," Toner said. "Transparency and rule of law are absolutely crucial and violence by any party will not help achieve the goals of the January 25 revolution."

In addition to discontent over serving justice to Mr Mubarak and stalwarts of his regime, the country is plagued by a dramatic surge in crime and divided by a debate on whether a new constitution should be drafted before or after parliamentary elections due later this year.

Many Egyptians also fear that Islamists are poised to dominate the country, taking advantage of the weakness of liberal and leftist groups born out of the uprising. Others are worried that remnants of Mr Mubarak's regime are undermining the nation.

The ruling military issued a statement on its Facebook page asserting the clashes were designed to "destabilise the country" and drive a wedge between the opposition and security forces. It called on Egyptians not to join the protests.

Security officials said at least 30 protesters were arrested and were being questioned by military interrogators.