Details added (first version was published at 19:58)
The United States condemned the outbreak of violence and intimidation on the streets of Cairo on Wednesday following Egyptian President Hosny Mubarak's announced plans to step aside, dpa reported.
"The United States deplores and condemns the violence that is taking place in Egypt, and we are deeply concerned about attacks on the media and peaceful demonstrators," White House spokesman Robert Gibbs said. "We repeat our strong call for restraint."
US President Barack Obama spoke Tuesday night with Mubarak after the Egyptian leader announced he will step aside in September, following more than a week of massive protests calling for him to resign.
Obama sent a clear message to Mubarak "that the time for change had come," Gibbs said.
"The conversation that the president had with President Mubarak was direct, it was frank, it was candid," Gibbs said.
Clashes between Mubarak supporters and the longtime ruler's opponents erupted Wednesday on Cairo's Tahir Square, which had been at the centre for the last nine days of mass protests against Mubarak's 30-year rule. At least one person has been killed and hundreds injured.
US State Department spokesman PJ Crowley said the "attacks" on the protesters are "dangerous" for the country and the people's aspirations for democratic reforms.
"The use of violence to intimidate the Egyptian people must stop. We strongly call for restraint," Crowley said.
The protests forced Mubarak to announce Tuesday night that he will not seek another re-election when his current term expires in September. Gibbs reiterated Obama's remarks, following Mubarak's announcement, that Egypt must move quickly into a democratic transition.
"The time for a transition has come, and that time is now," Gibbs said.
Obama did not directly say whether Mubarak should have immediately stepped aside, but reports suggested the White House would have preferred that Mubarak relinquish power to an interim government until elections could be held.
The Obama administration had initially struggled to establish a clear position, but as protests grew it became clear Mubarak could not hold onto power, and the US began calling for an "orderly transition."
The White House last week had expressed support for the democratic goals of the movement, but did not want to alienate Mubarak, a long- time US ally seen as a source of stability in the region.