In his first remarks since Mohammed Morsi's ouster, Egypt's military chief said on Sunday the armed forces acted according to the will of the people because the former Islamist government had stumbled.

Gen. Abdel Fattah al-Sisi made his comments on the eve of another round of mass protests by Morsi's Islamist supporters who have accused the military of staging a coup and demanded the reinstatement of Egypt's first democratically elected president.

Turkish Prime Minister Recep Tayyip Erdogan said Sunday that ousted Muslim Brotherhood leader Mohamed Morsi was the only legitimate president of Egypt in an interview with a Turkish newspaper.

"Currently, my president in Egypt is Morsi because he was elected by the people," he told the pro-government Today's Zaman. "If we don't judge the situation like that it is tantamount to ignoring the Egyptian people," he added.

Prominent liberal Egyptian leader Mohamed ElBaradei was sworn in on Sunday as Egypt's interim vice president for foreign relations, the presidency said in a statement, as Nabil Fahmy was appointed as foreign minister.

The appointment of ElBaradei, a former head of the U.N. nuclear watchdog and a Nobel peace laureate, follows the military overthrow of Islamist President Mohammed Morsi on July 3.

Investigators began questioning Egypt's ousted President Mohammed Morsi and members of his Muslim Brotherhood on Sunday over their involvement in a 2011 prison break, judicial sources told AFP.

The inquiry follows allegations that Morsi and senior Brotherhood members escaped from Wadi Natrun prison during the uprising that ended former president Hosni Mubarak's three-decade rule.

Egypt's new prime minister moved closer to forming a cabinet on Saturday, as prosecutors looked into criminal complaints against ousted Islamist president Mohammed Morsi and members of his Muslim Brotherhood.

Hazem al-Beblawi held talks with candidates for ministerial posts accompanied by vice president Mohammed ElBaradei, and the consultations will continue on Sunday.

Several thousand people protested in central Tunis on Saturday against the Egyptian army's overthrow of Islamist president Mohammed Morsi.

The protest was called by Tunisia's ruling Islamist Ennahda party.

Egypt's shattered economy was boosted this week by Gulf allies pledging billions of dollars in aid, but analysts say this simply buys time as political turmoil deepens its economic malaise.

The millions of ordinary Egyptians angered by record high unemployment, soaring inflation and chronic fuel shortages who took to the streets two weeks ago demanding Mohamed Morsi's resignation blamed him for letting the economy nosedive.

U.S. President Barack Obama on Friday spoke by phone with Saudi King Abdullah to discuss aid to Syrian opposition forces and to discuss the coup in Egypt, the White House said.

"The President and the King shared their perspectives on the situation in Syria and expressed their strong concerns about the impact of the conflict on the region," a White House statement said.

The U.N. refugee agency on Friday expressed deep concern over a new Egyptian visa requirement for Syrians and reports that Syrian refugees were being returned to their war-ravaged country.

"I appeal to the Egyptian authorities, as I have to all other governments in the world, to admit and protect all Syrians seeking refuge in their country," U.N. High Commissioner for Refugees Antonio Guterres said in a statement.

The United States on Friday urged the Egyptian military and interim leaders to free deposed president Mohammed Morsi for the first time since he was detained over a week ago.

State Department spokeswoman Jen Psaki said the United States agreed with Germany's earlier appeal for Morsi to be released and was "publicly" making the same request.