* Police break up pro-Brotherhood protest in Tahrir
* Constituent assembly edges closer to final draft
* Exiled Islamist says army has driven Egypt to "precipice"
Egyptian security forces fired teargas in Cairo's Tahrir Square to disperse anti-government protesters on Sunday, as a new constitution that reinforces the military's political power edged closer to approval.
The draft constitution reflects how the balance of power has shifted in Egypt since secular-minded generals deposed Islamist President Mohamed Mursi in July after mass protests against him. It contains language that could ban Islamist parties outright.
A major milestone in Egypt's political roadmap, the constitution must be approved in a referendum before new elections, which Mursi's Muslim Brotherhood, driven underground by security measures and a legal ban, is unlikely to contest.
"The people want to topple the regime," chanted several hundred protesters who descended on Tahrir Square, epicentre of the 2011 uprising against autocratic President Hosni Mubarak.
Though it only lasted about half an hour before security forces acted, it appeared to be the biggest protest by Brotherhood sympathisers in Tahrir since Mursi's fall. "With our blood and souls we sacrifice for you, Islam," chanted some.
One scaled a lamp post where he hung a picture of Mursi. Others flashed the four-finger hand sign denoting sympathy with the hundreds of Mursi supporters shot dead by the security forces when they broke up their Cairo sit-ins on Aug. 14.
Some of the protesters said they were not from the Brotherhood. "I want Sisi out and a real end to army rule," said Ramez Ibrahim, 32, a professor of political science, referring to armed forces chief General Abdel Fattah al-Sisi.
Army vehicles moved in to drive the demonstrators away and later sealed off the square completely. Some passersby shouted abuse at the protesters, others waved in support. Earlier, protesters set a police truck ablaze near Cairo University.
The government says it is determined to implement a law passed last week that heavily restricts protests. Criticised by the United States, the law has hardened fears of pro-democracy campaigners about the future of political freedoms in Egypt.
One of two leading secular activists detained for calling protests in defiance of the law was released on Sunday.
The 2011 Tahrir Square uprising awoke hopes of a new era of freedom in the most populous Arab nation. But three years of turmoil have made many Egyptians yearn for stability.
Sisi is seen as an army strongman and a front-runner for the presidency, though he has yet to declare his candidacy.
ASSEMBLY VOTES ON CONSTITUTION
Mursi's fall set off the bloodiest bout of internal strife in Egypt's modern history, with hundreds of his partisans killed and armed attacks on the security forces becoming commonplace.
Some 200 policemen and soldiers have been killed in what the military-backed government casts as a war on terrorism. The Brotherhood says it is peacefully resisting the army takeover.
A few hundred metres (yards) from Tahrir Square, the 50-member constituent assembly was voting on the draft constitution whose provisions include a ban on parties formed on a religious basis. Islamists have won all post-Mubarak national votes.
The assembly, chaired by former Arab League Secretary-General Amr Moussa, voted against five of the document's 247 articles, including one requiring parliamentary polls to be held before a presidential vote.
Some assembly members had called for presidential elections to be held before parliamentary ones, citing the weakness of secular political parties. The assembly, which is working to a Dec. 3 deadline, was to redraft the provision later on Sunday.
The draft constitution widens the already broad privileges enjoyed by the army by requiring the approval of the Supreme Council of the Armed Forces for the choice of a defence minister to serve for eight years from when the document is ratified.
It does not indicate how the minister of defence could be sacked or who has the authority to fire him.
The new constitution will replace one drafted by an Islamist-dominated assembly and signed into law by Mursi last year after it was approved in a referendum. The new text strips out Islamist-inspired additions introduced last year.
The Nour Party, an ultra-conservative Islamist party that backed Mursi's ouster, has described the draft as "satisfying".
"CONSTITUTION OF MINORITIES"
But one Mursi ally, Gamaa Islamiya leader Assem Abdel Maged, said it was a "constitution of minorities", and that the army had driven Egypt to the "edge of a precipice".
Speaking from exile in Qatar, the hardline Islamist said the army had sided with religious and social minorities, a reference to Christians and secular-minded Egyptians.
Abdel Maged fled to Doha after Mursi fell and is the first-high profile Islamist exiled since then to speak publicly. He is wanted on charges of inciting the killing of protesters.
"The army must review its position quickly because the country is on the edge of a precipice," Abdel Maged told Al Jazeera TV late on Saturday. He predicted things would get worse in Egypt and said protests would "break this coup".
Abdel Maged, who once shared a prison cell with al Qaeda leader Ayman al-Zawahri, was jailed for 25 years until 2006 for his role in the 1981 assassination of President Anwar Sadat and other crimes. After his Al Jazeera interview, Egypt's public prosecutor formally asked Interpol to arrest Abdel Maged.
Egyptian security officials said Abdel Maged had fled to Qatar by sea or via the border with Libya. Qatar is one of the few Arab states that was sympathetic to the Islamists during Mursi's year in power, supplying Egypt with billions of dollars in aid. Now relations between Qatar and Egypt are strained.
Abdel Maged, whose group fought an insurgency that was crushed by Mubarak in the 1990s, is still reviled as a terrorist by his foes. Gamaa Islamiya renounced violence a decade ago.