A senior US official was in Cairo Monday to press for a return to elected government following Mohamed Morsi's overthrow, as the Islamist leader's supporters and opponents readied rival rallies.

Under Secretary of State Bill Burns, the first senior US official to visit since the July 3 overthrow of Egypt's first freely elected president, flew in as the military-installed caretaker government tightened the screws on Morsi's backers, freezing the assets of 14 top Islamists.

Egypt's new leaders are pushing ahead with a transition plan for an interim government and fresh elections, but Morsi's Muslim Brotherhood defiantly insists on his reinstatement.

In the Sinai Peninsula, three factory workers were killed in a rocket-propelled grenade attack, medics said, in the latest in a spate of deadly attacks since Morsi's overthrow to hit the sensitive and increasingly lawless region bordering Israel.

Egypt's public prosecutor Monday ordered the arrest of seven senior Muslim Brotherhood and Islamist figures over the violence between Brotherhood supporters and opponents.

In his talks with interim military and civilian leaders, Burns was to push for "an end to all violence and a transition leading to an inclusive, democratically elected civilian government," the State Department said.

International concern is mounting over the continued detention of Morsi, who has been in custody since hours after the July 3 coup and was quizzed by prosecutors on Sunday over complaints of possible criminal offences.

Washington has still not decided whether he was the victim of a coup, which would legally require a freeze on $1.5 billion in desperately needed US military and economic assistance to Cairo.

Ashraf al-Arabi, a US-educated economist named planning minister in the interim government, said on Monday that aid from Arab states will carry Egypt through its transition period, and it does not need to restart negotiations with the IMF now.

AFP - Reuters