Egypt's presidency will appoint former finance minister Hazem el Beblawi as interim prime minister in a transitional government.
Acting head of state Adli Mansour also appointed former UN nuclear agency chief Mohamed ElBaradei as deputy to the president, responsible for foreign affairs.
Egypt's Islamist Nour Party has said it does not object to el Beblawi's nomination, but it was studying the likely appointment of el Baradei, the party's leader said in a statement.
Soldiers in gas masks on patrol in the Cairo suburb of Nasr CityThe news comes as Egypt is set to hold parliamentary elections by early 2014 as part of a swift timetable for social change.
According to an earlier decree issued by Mr Mansour, Egyptians will have five months to amend the constitution - suspended after Mohamed Morsi was removed from power in a military coup - before heading to the polls three months later.
Mr Mansour, a top judge who was picked by the military to steer the country through another period of transition, has promised a quick return to civilian rule.
However, Zaid al Ali, a constitutional lawyer, said the 33-article decree was "vague" enough to allow Mr Mansour to draw out the parliamentary vote.
Adli Mansour's decree comes after clashes between protesters and the army"The way it was worded suggests they plan to have the entire election within that timeframe," he said, but warned the interim president may only require candidates to start registering within the schedule set.
The decree was issued after 51 people were killed close to the gates of the Republican Guard officers' club in Cairo.
Many of those who died were supporters of Mr Morsi, who they believe is being held inside the building. Authorities have so far arrested 650 mostly pro-Morsi protesters after the killings.
Brotherhood leader Asem Abdel Maged delivers a speech to supportersMorsi's Muslim Brotherhood, which has led demonstrations against last week's military overthrow of the Islamist leader, have called for an "uprising" in response to the "massacre".
"Each province is organising funerals and rallies, and each province will have a central sit-in," Brotherhood spokesman Gehad El-Haddad said.
Video footage obtained by Sky News showed soldiers firing tear gas and volleys of automatic rifle fire during an apparent pre-planned operation to clear the streets of protesters.
A man holds a bloodstained shirt following earlier clashes with the armyA spokesman for the Nour Party, the country's second-biggest Islamist movement after the Muslim Brotherhood, said it would accept the choice of former finance minister Samir Radwan as interim prime minister.
Political sources said Radwan had emerged as the favourite for the post.
UN secretary general Ban Ki-moon has condemned the latest wave of bloodshed and called for an independent inquiry.
Supporters of Mohamed Morsi say their supporters were 'massacred'He urged Egyptians "to be mindful of the precarious path the country is now on and to do everything possible to avoid further escalation", his spokesman Martin Nesirky said.
Meanwhile, Middle East envoy Tony Blair has told Sky News there are "no easy solutions" to the crisis. Speaking to Sky's Dermot Murgnahan, Britain's former Prime Minister said Egypt needed to change its way of thinking for democracy to work.
"This wasn't a situation of people electing a Muslim Brotherhood government and then immediately the army stepping in," he said. "The army and people gave the government a chance to work but it lost support as was literally not governing.
"One the one hand you want to condemn the intervention of the military, on the other hand you think 'what else realistically could happen?' and how do we get the country back to stability?
"There is a big argument going on right across the Middle East right now of 'what is the proper place of religion in politics?' and how do you create a genuine democracy in these countries because democracy is not just a way of voting, it's a way of thinking."
Egypt stocks have risen during early trading following hopes a political solution to the crisis can be found that would allow an interim government to be formed before elections, after Cairo's benchmark index fell 3.6 percent on Monday.