Egypt's public prosecutor on Sunday ordered the freezing of assets belonging to 14 top Islamists, as the US dispatched its first senior official to Cairo since president Mohamed Morsi's ouster.
US Under Secretary of State Bill Burns will visit Egypt from Sunday to Tuesday, the State Department said, adding he would "underscore US support for the Egyptian people".
His trip comes amid growing pressure on Morsi's Muslim Brotherhood, which is in disarray with key figures either detained, on the run or keeping a low profile.
It also comes amid international calls for the release of the detained Morsi, Egypt's first freely elected president who was topped in a popularly backed military coup on July 3.
The Brotherhood has refused to join the new government headed by caretaker prime minister Hazem al-Beblawi who is pushing ahead with talks on forming his cabinet.
On Sunday, Beblawi appointed former ambassador to Washington, Nabil Fahmy, 62, as foreign minister, while prominent liberal leader Mohamed ElBaradei, 71, was sworn in as interim vice president for foreign relations.
Beblawi has said his cabinet's priorities would be to restore security, ensure the flow of goods and services and prepare for parliamentary and presidential elections.
The asset freeze is part of an investigation ordered by public prosecutor Hisham Barakat which affects nine Muslim Brotherhood leaders, including the group's general guide Mohamed Badie, and five Islamists from other groups including ex-militant faction Gamaa Islamiya, judicial sources said.
It relates to four deadly incidents since Morsi's overthrow, including clashes in Cairo last Monday in which dozens of people died.
The order comes a day after prosecutors received criminal complaints against Morsi, Badie and other senior Islamists, with a view to launching a formal investigation.
The complaints include spying, incitement to violence and damaging the economy, although the prosecutor's office did not say who made the allegations.
Morsi has not been seen in public since his ouster.
In his first public comments since removing the Islamist leader, military chief General Abdel Fattah al-Sisi said the army's leaders made the move after urging Morsi to hold a referendum on his presidency, which he rejected.
"The armed forces, with all its personnel and its leaders, decided without reserve to be at the service of its people and to empower their free will," he said in a statement.
The interim leaders say Morsi is being held in a "safe place, for his own safety," despite calls for his release by Germany and the United States, which has condemned a wave of arbitrary arrests of Brotherhood members.
Morsi's ouster plunged Egypt into violence.
In the worst single incident, clashes outside the Republican Guard headquarters last Monday killed 53 people, mostly Morsi supporters, in what the Brotherhood described as a "massacre" by the security forces.
Afterwards, the conservative Islamist Al-Nur party said it was pulling out of talks on a new government.
Human Rights Watch has called for an impartial investigation of military officers and police over the killings, saying, "witness after witness described the military shooting into the crowd, including at unarmed people".
In Cairo, Burns will meet interim officials as well as civil society and business leaders, and push for "an end to all violence and a transition leading to an inclusive, democratically elected civilian government," the State Department said.
Washington has struggled to define whether Morsi was the victim of a coup, which would legally force a freeze on some $1.5 billion in vital military and economic US assistance to Cairo.
In Brussels, EU foreign policy chief Catherine Ashton said the 28-member bloc was following developments in Egypt with "deep concern", while also calling for prompt elections and deploring recent violence.
Interim president Adly Mansour had set a timetable for elections by early next year, according to a roadmap drafted by the military, while Beblawi's new cabinet could be unveiled by Tuesday or Wednesday.
During his single year of turbulent rule, Morsi was accused of concentrating power in Brotherhood hands, sending the economy into free fall and failing to protect minorities.
But his supporters say his overthrow was a military coup and an affront to democracy, and are planning more mass protests on Monday.
Demonstrators will march to the Republican Guard headquarters, Brotherhood spokesman Tareq al-Morsi told AFP.
Rival protests are also planned on Monday in Tahrir Square and at the Ittihadiya presidential palace by the main coalition that had called for Morsi's resignation.