CAIRO (AP) -- Egypt's prosecutor general on Friday ordered a prominent youth leader detained for four days pending an investigation into accusations he incited anti-government violence, a security official said, in the latest case of a pro-democracy activist being held over similar charges.
The detention sparked a wave of anger among activists and the April 6 youth movement, which was at the forefront of the country's 2011 uprising, called for nationwide protests, including one in front of President Mohammed Morsi's house.
Meanwhile, Morsi's Islamist Muslim Brotherhood staged an anti-Israel rally, the first of its kind by the group since it rose to prominence in the wake of the revolt that ousted longtime autocrat Hosni Mubarak.
The security official said Ahmed Maher, a leader of April 6, was arrested at the Cairo airport as he returned from a trip to the United States.
According to the official, who spoke on condition of anonymity because he was not authorized to talk to the media, Maher is accused of "incitement" for actions at a March demonstration against the country's interior minister, when protesters hurled underwear at the minister's house to oppose a police crackdown on the activist group.
Maher was later taken to a heavily fortified prison in the Egyptian capital, the state-run MENA news agency said. Also late Friday, clashes broke out in downtown Cairo between rock-throwing protesters and security troops who fired tear gas at the demonstrators. The protesters were trying to bring down a cement wall blocking the entrance of a street leading up to the Interior Ministry building.
Maher's April 6 group was one of Morsi's top allies during his presidential campaign last year against a rival who was a Mubarak-era official the group feared would restore the former regime.
But since Morsi became president last June, April 6, like the rest of the liberal opposition, has been increasingly frustrated with the new government's practices and with what they see as the president serving his Islamist group's agenda in trying to monopolize power in the country.
Days before his arrest, Maher had expressed regret for his group's alliance with Morsi and the Brotherhood.
"Were we mistaken when we defended the Muslim Brotherhood at one point before the revolution and supported the Brotherhood candidate in the face of the military's and old regime's candidate," he wrote on the April 6 group's website.
"Now we are being treated as traitors and our image has been tarnished and we are sent to prisons by those we defended."
A myriad of charges and complaints have been leveled in recent months against activists, journalists and TV personalities, including well-known satirist Bassem Youssef, for insulting Morsi.
Earlier this month, authorities arrested Ahmed Douma, a leading activist, and referred him to court for allegedly insulting the president in a TV interview.
The crackdown comes at a time when Morsi's government is struggling to meet its promises to carry out reforms and improve Egyptians' quality of life. Along with lawlessness and economic woes, the country has witnessed a surge in sectarian tension, with the country's Christian minority increasingly feeling the heat of newly empowered hardline Islamists.
In the most recent example, security forces were put on alert Friday and deployed riot police to a southern village for fear of sectarian violence after a Coptic Christian tailor was killed by unidentified assailants, a security official said, speaking on condition of anonymity because they were not authorized to speak to the media.
Meanwhile, Amnesty International called on Egyptian authorities to release 24-year-old Coptic Christian schoolteacher Dimiana Abdel-Nour who is held for contempt of Islam. Abdel-Nour teaches history and geography in a southern village near the famed city of Luxor. She was accused by some students of allegedly showing contempt while talking about Islam in class last month.
Luxor prosecutor issued an arrest warrant against Abdel-Nour this week over allegations of proselytizing and of "defamation of religion." A court is scheduled to look into her detention on Saturday.
Amnesty's Hassiba Hadj Sahraoui said it was "outrageous that a teacher finds herself behind bars for teaching a class," adding that if Abdel-Nour had made a "professional mistake or deviated from the curriculum, an internal review would have sufficed."
Back in Cairo, the Brotherhood organized its first anti-Israel rally since it emerged as Egypt's most powerful political force in the wake of the Arab Spring uprising.
After Friday prayers at Al-Azhar mosque, the centuries-old seat of Sunni Muslim learning, demonstrators rallied in the street, chanted "the people want the destruction of Israel," denouncing recent Israeli airstrikes in Syria and the detention of a Palestinian Muslim cleric.