Supporters and opponents of Egyptian President Hosni Mubarak clashed in the streets of Cairo on Wednesday hours after the country’s leader said he would step down in September, a concession that failed to quiet calls for his immediate resignation.

Hundreds of pro-government supporters — some riding camels and horses — fought with protesters in the capital’s central square, where thousands were pushing ahead with demonstrations demanding Mubarak’s ouster.

“Pro-Mubarak demonstrators are facing off against anti-Mubarak demonstrators,” NPR’s Lourdes Garcia-Navarro reported from Tahrir Square, which has been the center of anti-government demonstrations for more than a week.

“They’ve been throwing rocks at each other,” she said. “At one point, the pro-Mubarak demonstrators led a charge into the crowd on horseback and on camel, and that created chaos.”

Protesters retaliated, dragging some from their mounts, throwing them to the ground and beating their faces bloody.

Garcia-Navarro said she saw several “injured people, covered in blood” and that as the clashes took place, army armored personnel carriers stationed at the square withdrew from the scene.

Almost immediately after Mubarak announced late Tuesday night that he would serve out the remaining seven months of his term and would not leave the country, groups of Mubarak supporters rarely seen during the week of anti-government protests took to the streets, some carrying knives and sticks.

Fighting between the two sides also erupted right after Mubarak’s address in the historic Mediterranean port of Alexandria.

Those calling for Mubarak to go have been out in Cairo and many other cities for more than a week, and they drew by far their largest crowd on Tuesday when at least a quarter million packed the central Tahrir, or Liberation, Square.

The crowds that assembled Wednesday were considerably smaller but no less energized than Tuesday’s show of force, when at least a quarter million packed the central Tahrir, or Liberation, Square. Angry opponents of Mubarak snatched posters of the president out of the hands of his supporters and ripped them to shreds.

The confrontations began after a military spokesman went on national television and asked the opposition protesters to disperse so that life in Egypt could go back to normal.

“The army forces are calling on you,” the spokesman, Ismail Etman, said in a statement directed at the anti-government protesters. “You began by going out to express your demands and you are the ones capable of restoring normal life.”

But opposition forces — a disparate coalition of factions including the fundamentalist Muslim Brotherhood and Nobel peace laureate Mohamed ElBaradei — called for demonstrations to continue.

President Obama spoke with Mubarak by phone shortly after the Egyptian leader’s announcement aired late Tuesday.

“What is clear and what I indicated tonight to President Mubarak is my belief that an orderly transition must be meaningful, it must be peaceful and it must begin now,” Obama said. “Through thousands of years, Egypt has known many moments of transformation. The voices of the Egyptian people are telling us this is one of those moments, this is one of those times.”

A former U.S. ambassador to Egypt, Frank Wisner, met with Mubarak earlier and made clear that it is the U.S. “view that his tenure as president is coming to a close,” according to an administration official, who spoke on condition of anonymity.

The continued chaos in Egypt has taken a toll on the country’s economy, with Moody’s on Wednesday cutting its sovereign rating to Ba2, citing the unrest. The downgrading will make it harder for Egypt to borrow, which could further damage the economy and contribute to further unrest.

NPR’s Lourdes Garcia-Navarro and Corey Flintoff reported from Cairo for this story, which contains material from The Associated Press. Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.