Fresh from toppling the country's first democratically elected leader, Egypt's military risked further outrage from the Muslim Brotherhood by arresting the group's Supreme Guide as he was staying in a resort by the Mediterranean coast.
Mohammed Badie, the Brotherhood's spiritual leader, was arrested at an acquaintance's villa in Mersa Matruh in northwest Egypt. He was then flown to Cairo on a military helicopter, according to security officials.
"This is even worse than it was for us under Hosni Mubarak," said Amr Darrag, a leading Brotherhood official.
The development came as the military oversaw the swearing-in of Egypt's interim President just 24 hours after it toppled Mohammed Morsi. Adly Mansour, formerly a leading judge, will preside over a provisional Government until elections, although no date has been set.
Mansour had been one of the candidates put forward by the opposition groups that spearheaded this week's insurrection against Morsi.
In a ceremony aired live on state television, Mansour said there would be "no exclusion of anyone" under his rule. As news spread of the anti-Islamist crackdown, he offered an olive branch to the Muslim Brotherhood and said he wanted them integrated into the nation. He added that the June 30 revolt had "corrected the path of the glorious revolution" which took place 2 years ago.
The prospect of compromise was scotched by the Brotherhood. "We declare our complete rejection of the military coup staged against the elected President and the will of the nation," it said.
Badie's arrest was part of a wider crackdown against the Brotherhood that saw the authorities issue a wanted list for 200 of its members.
At least a dozen Brotherhood officials have now been detained, according to one NGO director, although another human rights worker said the number of Islamists arrested could be nearly three times that figure.
Prosecutors also announced that Khairat el-Shater, the leading Brotherhood strategist who almost ran for president in 2012, is wanted and faces arrest.
Meanwhile, Morsi is being held with his aides at a military intelligence facility, according to a security source who spoke to Reuters.
Egypt's state news agency reported that officials issued the warrants for Badie and Shater in connection with the deaths of eight protesters killed during clashes outside the Brotherhood's headquarters on Monday.
The crackdown came after authorities moved to silence the Islamist media in the wake of Thursday's military coup.
Following the dramatic moment that General Abdulfattah al-Sisi, the head of Egypt's armed forces, announced the military was taking over, the Muslim Brotherhood's Misr 25 channel went off air.
Other Islamist stations were also cut off and their owners reportedly detained. In addition, travel bans have been slapped on Morsi and other leading figures from the Brotherhood.
After the general's address, clashes between pro and anti-Morsi factions across Egypt left 10 people dead and more than 400 injured. Security forces rounded up Saad el-Katatni, the former Speaker of Parliament who was also head of the Brotherhood's political wing, while a deputy leader of the group, Rashad al-Bayoumi, was also arrested. Both men were reportedly being held at Cairo's Tora Prison.
Some analysts have speculated that the Brotherhood may resort to violence, yet the Islamist group has so far eschewed any outright call for revenge.
Deserted almost entirely by its political allies, bereft of its arrested leaders and loathed by millions, it probably feels unable to respond adequately, according to the Egypt expert Nathan Brown.
"The Brotherhood is standing alone," he said. "It's an organisation which isn't accepting what's happening but is not doing anything to resist, apart from complaining."