CAIRO // Five months of relative calm in Egypt has been shattered with protesters and authorities once again clashing in Tahrir Square.
Protests and marches erupted throughout Tuesday night and yesterday amid clouds of tear gas and stone throwing, as groups demanded a quicker trial for the former president, Hosni Mubarak, and justice for families of those who died during the revolution.
The streets were a scene of devastation, littered with rocks, glass and smashed up cars. More than 1,000 people - protesters and police officers - were injured, according to the state news agency Mena. Security forces arrested at least nine people.
The sudden outburst of violence was a sign of the long-simmering tensions with the interim government, led by the military, and analysts said it could push back Egypt's transition to stability and put pressure on officials to make greater reforms.
"These events show that the transition and the unrest is far from over," said Elijah Zardwan, an Egypt analyst with the International Crisis Group. "There's still a lot of anger and dissatisfaction and it has been very close to the surface."
The initial cause of the latest violence was unclear, but protesters said a group of families of victims, known as the "martyrs", of the revolution began protesting outside the Ministry of Interior after they were denied entry to an event commemorating the victims.
The government countered those claims, saying the events were precipitated by provocateurs who were not invited to the event and intended to disrupt the goodwill between the people and the military.
The Supreme Council of the Armed Forces, which took over the government after Mr Mubarak stepped down as president in February, said on its Facebook page that the events "had no justification other than to shake Egypt's safety and security in an organised plan that exploits the blood of the revolution's martyrs and to sow division between the people and security apparatus".
Early yesterday morning, the protesters marched to Tahrir Square, the centre of protests during the revolution, but were met by police who fired tear gas.
By 10am, a front line had moved to Mostafa Mahmoud Street in front of the American University of Cairo building near Tahrir Square. Hundreds of protesters, many wearing goggles and scarves to protect themselves from the tear gas, pushed against a line of black-clad riot police.
Ahmed Ali, a 26-year-old Vodafone employee, said he was on his way to work in downtown Cairo when he came across the protests and joined their ranks.
"This is the worst it has been since the revolution," he said, as people chanted about the military's slowness to bring Mr Mubarak to trial and attempts hijack the country. "People want justice," he said.
There was an ebb and flow of the clashes with the police, as people fled canisters lobbed into crowds. But, with stronger numbers, the protesters pushed themselves all the way back to the ministry of interior, about a 10-minute walk. At one point, military police officers with red berets attempted to calm protesters but they were overrun and retreated behind the riot police.
There was widespread discussion of military and police conspiracies with the former regime.
Field Marshal Mohammed Hussein Tantawi "and Mubarak are very close", said Mohammed Arafat, a 27-year-old tour guide.
"Egyptian people will not let them take away the revolution."
Some young men prepared Molotov cocktails made with fuel taken from cars along the way and threw them at police.
One person accidentally set himself on fire and was rescued by people nearby who smothered the flames.
A steady flow of motorcycles brought the injured from the front-line back to Tahrir and nearby hospitals to receive medical treatment.
Crowds began to disperse late yesterday afternoon, but there were calls for more gatherings at Tahrir Square and around the city.
Sitting on a curb, 17-year-old Mohammed Mahmoud Ahmed, said he had come across the protest earlier in the day.
"At first, I wanted to see," he said. "I am reading from the Quran and hoping it stops."
Just then, there was the familiar hollow "thunk" sound of canisters being fired by the police. Mr Ahmed began running and disappeared into the clouds of gas.