More than 750 people have died in four days of violence this week after a bloody crackdown in Cairo on supporters of ousted Islamist president Mohamed Morsi.
The bloodshed has been widely condemned by the international community, and Carter yesterday urged Egyptian security forces to show greater restraint.
"I am deeply concerned that the ongoing violence in Egypt is rapidly eroding the chances for dialogue and a road to reconciliation," Carter said in a statement.
"The recent confrontations have already resulted in hundreds of deaths, and turning against one another will only lead to more pain and suffering."
President Barack Obama has faced criticism in the United States for his handling of the Egypt crisis. He has resisted cutting aid to Egypt's military.
A recent Washington Post editorial said Obama's administration had been "complicit" in the crackdown because it had shown to Egypt's rulers "that its warnings were not credible.