Egypt's authorities yesterday formally detained Mohamed Morsi on suspicion of collaborating with Palestinian militants in murdering policemen and staging prison breaks, as tens of thousands of the deposed president's supporters and opponents staged rival rallies.
Morsi's detention, under a court order, for a renewable 15 days further ramped up tension as those applauding the decision and those angrily demanding the Islamist leader's reinstatement flooded various parts of Cairo.
The Arab world's most populous country has been convulsed by violence for the past three weeks, with some 200 people killed since Morsi's ouster by the army on July 3, many in clashes between his Islamist supporters and his opponents.
Clashes broke out in Cairo's Shubra neighbourhood in the early afternoon, leaving 10 people wounded as the two sides traded stones.
Another 15 people were wounded in clashes in the Mediterranean city of Alexandria, the health ministry said. Police broke up the clashes with tear gas, state media reported.
But the overwhelming number of marches remained peaceful, with thousands of Morsi's supporters gathering in a north Cairo square before setting off through the streets.
At Cairo's Tahrir Square, tens of thousands of anti-Morsi supporters gathered in response to a call by the army chief General Abdel Fattah al-Sisi on Egyptians to show their support for a security clampdown on "terrorism".
The protesters waved Egyptian flags and held up posters of Sisi, who served as Morsi's defence minister before ousting him.
A leader of Morsi's Muslim Brotherhood, Essam al-Erian, said in a statement Islamists would respond to the detention of their leader with "peaceful marches".
The Brotherhood however reacted angrily to his detention order, saying it smacked of tactics used by the regime of Hosni Mubarak, Egypt's long-time strongman toppled in a popular uprising in 2011.
The accusations against Morsi include conspiring with Palestinian Hamas militants in attacks that killed policemen and prison breaks during the revolt against Mubarak, in which Morsi escaped along with other political inmates.
He is also accused of "premeditated murder of some prisoners, officers and soldiers, and kidnapping officers and soldiers," state news agency MENA said.
Morsi is suspected of conspiring to "storm prisons and destroy them..allowing prisoners to escape, including himself."
Detention orders of the type ordered by the court are usually followed by moving the suspect to a prison. The military has so far kept his whereabouts secret to avoid attracting protests by his supporters.
Gehad El-Haddad, a Brotherhood spokesman, denounced the detention order, saying Mubarak's regime was "signalling 'we're back in full force'."
A court had on June 23 said Hamas militants facilitated the escape of prisoners during the tumultuous 18-day uprising that forced out Mubarak.
Hamas, an offshoot of the Muslim Brotherhood which supports the Gaza militant group's fight against Israel, also denounced Morsi's detention.
"Hamas condemns this move since it is based on the premise that the Hamas movement is hostile," spokesman Sami Abu Zuhri told AFP.
Morsi's election victory in June 2012 had been hailed by Hamas as a triumph for Islamists.
He helped negotiate a truce to halt fighting between Israel and Hamas in November on favourable terms for the Islamists, but also oversaw the closing of smuggling tunnels to Gaza.
The military has reportedly given Morsi's backers until the end of Friday to end sit-in protests they began after the army deposed him.
The Brotherhood and allied Islamist groups for their part have vowed to press their protests until he is reinstated.
Western nations are watching the crisis in Egypt with growing unease, fearing the military's vow to return the nation to democracy may be little more than a fig leaf to mask a prolonged power grab.
The United States has decided not to term the army's overthrow of Morsi a "coup," which would trigger an automatic freeze of some $1.5 billion in aid, a US official said in Washington on Friday.
But the US did finally send the interim leaders a veiled warning on Wednesday by suspending the delivery of four promised F-16 fighter jets.
"The interim government's strategy clearly consists of politically sidelining the Muslim Brotherhood until the elections," said German Middle East expert Michael Lueders.
London-based rights group Amnesty international criticised Sisi's call for rallies, in a statement Thursday.
"Given the security forces' routine use of excessive force, such a move is likely to lead to yet more unlawful killings," said Hassiba Hadj Sahraoui, Amnesty's deputy director of its Middle East and North Africa programme.