The Egyptian military has moved in to break up street battles between supporters and opponents of deposed Egyptian President Mohamed Morsi.
Armored vehicles moved across the 6th of October Bridge in central Cairo on Friday with anti-Morsi protesters hanging on.
A military spokesman tells the French news agency that soldiers are not taking sides but are moving in to protect lives.
Members of the rival camps fought across Cairo and other cities including Alexandria Friday, throwing rocks and fireworks and engaging in fistfights. State-run television says at least 17 people have been killed.
The United States and the United Nations urged Egyptians to reach a peaceful end to the crisis and avoid violence.
U.N. Secretary General Ban Ki-moon said, "This is a critical juncture in which it is imperative for Egyptians to work together to chart a peaceful return to civilian control, constitutional order, and democratic governance."
In Washington, State Department spokesperson Jen Psaki said the United States calls on "all Egyptian leaders to condemn the use of force and to prevent further violence among their supporters."
Earlier Friday, government troops opened fire on Morsi supporters who tried to march on the Defense Ministry headquarters.
The army arrested Morsi and other leaders of the Egyptian Muslim Brotherhood on Wednesday and suspended the constitution. The army said its action was prompted by the risk of a popular uprising.
The military has sworn in a senior jurist, Adly Mansour, as interim president.
The opposition has accused Morsi of betraying the 2011 revolution that toppled Hosni Mubarak.
The military and Egypt's former opposition groups have called for reconciliation as the military moves forward with its so-called road map to restore democratic civilian rule.
Muslim Brotherhood leaders have slammed the military for shutting down its official television channel and newspaper and several other Islamist media outlets. The group said in a statement that the moves bring Egypt "back to the era of repressive practices, dictatorship, and corruption."
Judicial officials say they will open an investigation next week against Morsi and other Brotherhood members on charges of "insulting the judiciary."
"We are not in a battle with the Egyptian armed forces; our battle is with those who orchestrated the coup, until they go back on it and free President Morsi from his captivity and restore him to the presidency," said Mohammed el-Beltagy, General Secretary of the Islamist Freedom and Justice Party.
Muslim Brotherhood supporter Safwat Hegazy said the group hopes to overwhelm the military by the sheer force of numbers.
"This is the Egyptian people's million man march to regain legitimacy from the traitors, from the military council," said Hegazy.