Saudi Arabia's King Abdullah has sent a message of congratulations to the head of the Egyptian Constitutional Court, Adli Mansour, for being appointed interim head of state, the Saudi state news agency SPA reports.
"In the name of the people of Saudi Arabia and on my behalf, we congratulate your leadership of Egypt in this critical period of its history. We pray for God to help you bear the responsibility laid upon you to achieve the ambitions of our brotherly people of Egypt," the message said.
The Muslim Brotherhood tells ITV News they are against violence but will "pay the price of their blood" to restore their ousted president.
Egypt's army has named two further officials in the transitional government as its supporters and opponents vowed to stay on the streets.
There has been outrage in Egypt after 51 people were killed near an barracks where ousted President Mohamed Morsi is thought to be held.