The family of ousted president Mohamed Morsi vowed Monday to press charges against the powerful military commander who forced him from power.

Osama Morsi, the son of the former president, spoke at a news conference in downtown Cairo, as hundreds of protesters massed in front of the attorney general’s office down the street, chanting against the military officers who removed Morsi, Egypt’s first democratically elected president, in a July 3 coup.

The younger Morsi on Monday called his father’s detention by the armed forces a “kidnapping” and a “crime.” He said the secretive conditions of the detention violated the standards of international law and underscored the “militarization” of Egypt since the coup, despite the appointment of a civilian president and prime minister.

“I challenge the attorney general to [show he] knows where President Morsi is being detained,” Osama Morsi said.

Egypt’s military has held Mohamed Morsi and a number of his top aides from the Muslim Brotherhood incommunicado in an undisclosed location since Morsi’s ouster. Asked by one reporter Monday whether his father was dead or alive, Morsi’s son said, “I don’t know any more than you do.”

The family said it has launched legal action against the chief of Egypt’s armed forces, Gen. Abdel Fatah al-Sissi, and his collaborators. The process at home is unlikely to yield results in a country where the military has operated with impunity and secrecy for decades.

“We are in the process of taking legal action through international and local courts,” said Shaimaa Mohamed Morsi, the ousted president’s daughter. The family did not specify the international courts, but Morsi supporters in the past have talked about approaching the United Nations and the International Criminal Court.

Supporters of the ousted president have staged demonstrations across the country over the past three weeks. On Monday, demonstrators clashed with anti-Morsi Egyptians and security forces in separate incidents across downtown Cairo, outside the Defense Ministry and in an industrial province north of the capital. At least three people were killed, the state-run Middle East News Agency reported.

In Egypt’s Sinai Peninsula, a lawless territory flush with weapons and militants on the border with Israel and the Gaza Strip, violence has raged nearly every day since Morsi’s fall, highlighting the deteriorating security situation there.

Armed men have launched dozens of attacks on police and military checkpoints, killing at least 14 members of the security forces and seven civilians since early this month. Battles raged between militants and security forces in North Sinai’s two biggest towns late Sunday, injuring seven troops and a civilian. At least two more security troops were wounded in a shooting Monday afternoon, the state news wire reported.

Egyptian state media have blamed the attacks on militants backed by the Muslim Brotherhood, which supports Morsi.

On Monday, a Cairo-based polling organization released the results of a nationwide survey on the country’s unrest. Seventy-one percent of the roughly 2,000 Egyptians surveyed said they oppose the pro-Morsi demonstrations, according to the nonpartisan polling organization Baseera. About 20 percent of those surveyed said they support the demonstrations; 9 percent remain undecided.

Confusion about Morsi’s whereabouts and legal status in the aftermath of his ouster have added fuel to the street battles and have permeated the highest echelons of power, as the nation lurches through an uncertain transitional period.

The country’s state-run al-Ahram newspaper ran a series of sensational headlines across its front page Monday, including “details of the American conspiracy for Egypt in the last hours of the Brotherhood’s rule” and alleged charges against the ex-president, which it said included “spying.”

But the military quickly slammed the headlines as false, and the attorney general’s office summoned the paper’s editor in chief on Monday.

The Muslim Brotherhood’s Anti-Coup, Pro-Democracy Alliance, set up after Morsi’s ouster, called the headlines “utter lies.”

Essam el-Erian, a Muslim Brotherhood leader, called on Morsi’s supporters Monday to take their demonstration to the U.S. Embassy in protest of Washington’s alleged support of the coup.

Anti-American rhetoric has also been ubiquitous at anti-Morsi demonstrations, where opponents of the Islamist leader have accused Washington of conspiring to keep the Muslim Brotherhood in power.