And he took aim at Western critics of the Islamists. “The silence of all of those voices with an impending military coup is hypocritical,” Mr. Haddad wrote, “and that hypocrisy will not be lost on a large swath of Egyptians, Arabs and Muslims.”

In Egyptian Sinai just hours later, thousands of Islamists rallied under the black flag of jihad and cheered widely at calls for “a war council” to roll back Mr. Morsi’s ouster. “The age of peacefulness is over,” the speaker declared in a video of the rally. “No more peacefulness after today.”

“No more election after today,” the crowd chanted in response.

After a night of deadly clashes at Cairo University that accompanied the takeover, some ultraconservative Islamists gathered there said their experiment in electoral politics — a deviation from God’s law to begin with — had come to a bad end.

“Didn’t we do what they asked,” asked Mahmoud Taha, 40, a merchant. “We don’t believe in democracy to begin with; it’s not part of our ideology. But we accepted it. We followed them, and then this is what they do?”

In Syria, where the Egyptian Muslim Brotherhood once hoped to provide a model of moderation and democracy, some fighters battling President Bashar al-Assad now say it is the other way around. Egyptian Islamists “may have to pursue the armed option,” said Firas Filefleh, a rebel fighter in an Islamist brigade in Idlib, in northern Syria. “That may be the only choice, as it was for us in Syria.”

In the United Arab Emirates, where the authoritarian government just sentenced 69 members of a Brotherhood-linked Islamist group to prison in an effort to stop the spread of Arab spring revolts, Islamists said the crackdowns were driving a deeper wedge into their movement.

“The practices that we see today will split the Islamists in half,” said Saeed Nasar Alteneji, a former head of the Emirates group, the Islah association. “There are those who always call for centrism and moderation and peaceful political participation,” he said. “The other group condemns democracy and sees today that the West and others will never accept the ballot box if it brings Islamists to power.”