Egypt's prosecutor ordered the arrest on Wednesday of the leaders of ousted President Mohamed Morsi's Muslim Brotherhood, charging them with inciting violence in a clash that saw troops shoot 55 Morsi supporters dead.
A week after the army toppled Egypt's first democratically elected leader, bloodshed has opened deep fissures in the Arab world's most populous country, with bitterness at levels unseen in its modern history.
Brotherhood spokesman Gehad El-Haddad said the announcement of charges against leader Mohamed Badie and several other senior figures was a bid by authorities to break up a vigil by thousands of Morsi supporters demanding his reinstatement.
This week's unrest has alarmed Western donors and Israel, which has a 1979 peace treaty with Egypt. Washington, treading a careful line, has neither welcomed Morsi's removal nor denounced it as a "coup", which under U.S. law would require it to halt aid including the $1.3 billion it gives the army each year.
The Brotherhood's downfall has however been warmly welcomed by three of the rich Arab monarchies of the Gulf, who showered Cairo with aid to prop up the collapsing Egyptian economy.
Kuwait promised Egypt $4 billion in cash, loans and fuel on Wednesday, a day after Saudi Arabia pledged $5 billion and the United Arab Emirates offered $3 billion.
The Brotherhood leaders were charged with inciting violence in Monday's shootings, which began before dawn, when the Brotherhood says its followers were peacefully praying. The army says terrorists provoked the shooting by attacking its troops.
Haddad said the Brotherhood leaders had not been arrested and some were still attending the protest vigil at Rabaa Adawiya mosque. The charges against them were "nothing more than an attempt by the police state to dismantle the Rabaa protest".
"What can we do? In a police state when the police force are criminals, the judiciary are traitors, and the investigators are the fabricators, what can one do?"
In addition to Badie, prosecutors ordered the arrest of others including his deputy, Mahmoud Ezzat, and outspoken party leaders Essam El-Erian and Mohamed El-Beltagi. Khairat El-Shater, another senior leader, was held last week.
The prosecutor also ordered 206 Brotherhood activists arrested after Monday's violence to be detained for a further 15 days on accusations of involvement in the killings. It released 464 others who had been detained, on bail of about $300 each.
Egyptians have hoped the start of Ramadan, the Muslim fasting month, would cool passions, but it has been overshadowed by rancor.
Thousands of Brotherhood supporters braved brutal summer heat to maintain their outdoor protest vigil despite the fast, clustering in tents to protect themselves from sun during daylight hours when Islam forbids eating food or drinking water.
Some milled about, others staged small marches. A list was posted at the camp bearing the names of the more than 650 people arrested following Monday's "massacre".
Despite the violence that followed Morsi's removal, the interim authorities are proceeding with the army's "road map" to restore civilian rule. On Tuesday they named 76-year-old economist Hazem el-Beblawi as acting prime minister.
Beblawi told Reuters he would start selecting ministers and would begin by meeting liberal politicians Mohamed ElBaradei and Ziad Bahaa el-Din. ElBaradei, a former U.N. diplomat, has been named vice president. Bahaa el-Din, a former head of Egypt's investment authority, has been touted for senior posts.
Both are prominent figures in the National Salvation Front, the main secularist group that led protests against Morsi.
They also support a stalled $4.8 billion loan deal with the International Monetary Fund, which would require Egypt to make politically painful reforms to subsidies for food and fuel that support its 84 million people but drain its finances.
Beblawi accepted that it would be a challenge to find a cabinet line-up with universal support. "I don't believe that anything can have unanimous approval," he told Reuters.
Beblawi has indicated he would be open to offering cabinet posts to Islamists, including Brotherhood figures. The Brotherhood says it will have nothing whatsoever to do with a government of what it calls a "fascist coup".
The promised $12 billion in aid from the Gulf states will go a long way to easing a deep economic crisis that has driven Egypt's finances to the brink during two and a half years of instability since autocrat Hosni Mubarak was swept from power.
The funds also reduce the incentive for Egypt to make the reforms the IMF says are needed to stabilize public finances, draw investment and rekindle economic growth.
In other steps on their "road map", the authorities have announced a temporary constitution, plans to amend it, and a timetable for elections beginning in about six months.
Those moves already demonstrated the difficulty achieving political consensus, even among Morsi's opponents. The secularist NSF initially rejected the interim constitution, as did Islamists and others, although on Wednesday the NSF withdrew its rejection and issued a new, milder criticism.
On Wednesday, the authorities also named a chief prosecutor, replacing Morsi's appointee who was pushed out last week by a court that briefly reimposed his Mubarak-era predecessor.
With the Brotherhood sidelined, the authorities are courting the second largest Islamist group, the ultra-orthodox Nour Party, to demonstrate that Islamists will not be repressed as they were under decades of military-led rule.
Nour officially withdrew from politics in response to Monday's violence but has said it does not object to Beblawi's appointment and will assist his government.
Nour spokesman Nader Bakkar said on Wednesday the group would not accept posts in the new cabinet but would offer "consent and advice to help the cabinet pass through the transition period as soon as possible and with minimum damages".
"We are waiting to help. We are ready to advise but for the time being we still take the decision not to participate in the political process until the judiciary committee gives its report about what happened (on Monday)."
Bloodshed has abated since Monday's incident, the deadliest since Mubarak's fall, apart from a 2012 soccer stadium riot.
However, there are fears that the political violence could lead to a breakdown in security, especially in the lawless Sinai peninsula region bordering Israel.
Two people were killed and six wounded overnight when Islamist militants attacked a Sinai checkpoint.
On Tuesday, Israeli troops found the remains of a rocket they believe was fired across the border from Egypt.
Reporting by Maggie Fick, Alexander Dziadosz, Tom Perry and Shadia Nasralla; Writing by Peter Graff, editing by Peter Millership