The process of restoration is complicated by deadly protests and a political stalemate with powerful Islamist groups.
Interim head of state Adli Mansour, the burly judge leading the army-backed administration, swore in 33 mainly liberal and technocratic ministers at the presidential palace on Tuesday.
He did not include a single minister representing either of Egypt's main Islamist groups that have won five straight elections since 2011.
Islamist President Mohamed Morsi was ousted by the military on July 3 after-millions took to the streets to demand his resignation.
Morsi's Muslim Brotherhood movement insists he be returned to power before it joins the political process.
The Brotherhood rejected the interim government led by Mansour and Prime Minister Hazem el-Beblawi, a veteran liberal economist.
Confrontations
"It's an illegitimate government, an illegitimate prime minister, an illegitimate cabinet," said Brotherhood spokesperson Gehad el-Haddad.
"We don't recognise anyone in it. We don't even recognise their authority as representatives of the government."
The ministers took up their posts hours after seven people were killed and more than 260 wounded when Brotherhood supporters clashed with police in central Cairo and nearby Giza.
The deaths took the number of people killed in clashes since Morsi's overthrow to at least 99.
The confrontations are increasingly polarising society between those who support the military intervention and those who oppose it.
As well as violence and political infighting, the interim government must also drag the Egyptian economy out of its torpor, after two and a half years of upheaval left state coffers and food stocks running dangerously low.
Economy needs fixing
Saudi Arabia, the United Arab Emirates and Kuwait – rich Gulf Arab monarchies happy to see the fall of the Brotherhood – have promised a total of $12-billion in cash, loans and fuel.
But investors are sceptical that major reforms can be enacted before a permanent government is in place.
Parliamentary elections are expected to be held in about six months.
New Planning Minister Ashraf al-Arabi has said Arab aid would sustain Egypt through its transition and that it did not need talks with the International Monetary Fund on a stalled loan.
Egypt sought $4.8-billion in IMF credit last year, but months of talks on the loan stalled with the government unable to agree on cuts in unaffordable subsidies for food and fuel.
In a development welcomed by investors, Mohamed Abu Shadi, formerly a senior interior ministry official responsible for investigating supply crimes, became supply minister.
Analysts said his appointment signalled a desire to clamp down on the theft of subsidised fuel, gas and bread and to reform an unwieldy state subsidy scheme that accounts for about a quarter of the budget.
"I see it as a signal of a very strong state," said John Sfakianakis, chief investment strategist at Masic, a Saudi-based investment firm.
"They want to stop leakages in the supply system." – Reuters