President Barack Obama has ordered a review of U.S. aid to Egypt, after that country's military ousted democratically elected President Mohamed Morsi.
In a statement, Mr. Obama said he was "deeply concerned" about the military's decision and called for a return to democracy as soon as possible in Egypt, a long-time U.S. ally.
He also urged Egypt's military to ensure that the rights of civilians are protected during the transition.
United Nations chief Ban Ki-moon described the upheaval in Egypt as a "volatile situation" and called for a return to civilian rule "as soon as possible." He said he continues to stand with the aspirations of the Egyptian people.
NATO Secretary-General Anders Fogh Rasmussen said he is "gravely concerned" about Egypt. He urged all sides to exercise restraint.
European Union foreign policy chief Catherine Ashton urged all sides to "rapidly return to the democratic process."
Turkey, an ally of Egypt that recently struggled with its own anti-government protests, also expressed concern. At a Thursday news conference, Foreign Minister Ahmet Davutoglu said Mr. Morsi's ouster by the military was "unacceptable" and "extremely alarming."
African Union officials say the 54-nation alliance will meet soon to consider whether it will suspend Egypt's membership.
In Tunisia, the birthplace of the Arab Spring uprisings, the ruling Islamist Ennahda party called the turn-over in Egypt a "military coup against electoral legitimacy."
But leaders in Saudi Arabia sent messages of congratulations to Egypt. Qatar said it will continue to support the will of the Egyptian people.
The United Arab Emirates also voiced support for the transition. UAE President Sheikh Khalifa bin Zayed al-Nahayan congratulated Egyptian chief justice Adly Mansour, who has been sworn in as Egypt's interim leader.
Embattled Syrian President Bashar al-Assad welcomed the removal of Mr. Morsi. In a state media report, he said that after Mr. Morsi's year in office the Egyptian people had uncovered what he called the "lies" made by the ousted leader's Muslim Brotherhood movement.
In Russia, the foreign ministry called for restraint and said all "political forces" in Egypt should be guided by higher national interests.