"This is an incredibly complex and difficult situation," White House spokesman Jay Carney told reporters Monday "President Obama made clear our deep concern about the decision made by the Egyptian armed forces to remove President Morsi from power and to suspend the constitution. It is also important to acknowledge that tens of millions of Egyptians have legitimate grievances with President Morsi's undemocratic form of governance and they do not believe that this was a coup."
The Washington Post reported the political wing of Egypt's Muslim Brotherhood -- Morsi's party -- called for a popular uprising against the military after soldiers fired on supporters of the ousted president gathered outside the building where they believe Morsi is being detained.
State-run television said 51 people were killed and 435 were wounded in the shooting. Mahmoud Zaqzooq, a Muslim Brotherhood spokesman, said 53 were fatally shot, including five children.
Muslim Brotherhood officials and several witnesses said troops opened fire unprovoked as the protesters recited dawn prayers, the Post said. However, a military spokesman said armed pro-Morsi supporters attacked troops at the headquarters, killing one soldier, and the military responded with force afterward.
In Washington, Carney said the administration was reviewing the situation in Egypt carefully and any quick decision about Morsi's removal last week "is not in our interests."
"[We] need to be mindful of our objective here, which is to assist the Egyptian people in their transition to democracy," he said.
At stake is about $1.3 billion in military aid. U.S. law states financial assistance to the country must be cut off if it is determined Morsi was removed in a military coup. Egyptian officials said what happened Wednesday didn't result from a military coup but because of a popular uprising.
"We call on the military to use maximum restraint responding to protesters, just as we urge all those demonstrating to do so peacefully," Carney said. "We also condemn the explicit calls to violence made by the Muslim Brotherhood."
The administration urged political, military and other leaders to prioritize efforts to "bridge Egypt's deep divisions" because the country's stability and "democratic political order" are at stake.
"The United States is not aligned with, nor is it supporting any particular political party or group," Carney said. "We remain actively engaged with all sides, and we are committed to supporting the Egyptian people as they seek to salvage their nascent democracy."
In Monday's violence, officials said the army arrested more than 200 Muslim Brotherhood members armed with "large quantities of firearms, ammunition and Molotov cocktails," Ahram Online reported.
The Freedom and Justice Party of the Muslim Brotherhood said in its statement the army used "live bullets against thousands of peaceful protesters in front of the Republican Guard Club while performing prayers ... a gruesome massacre in every sense of the word."