CAIRO — Tumultuous efforts to draft a new constitution for Egypt rushed toward a conclusion Thursday as Islamists who dominate the council writing the new document called for a snap vote amid widespread protests against the Muslim Brotherhood-backed president.

The move was seen by some critics of President Mohamed Morsy as an effort by the Muslim Brotherhood to hijack the constitution.

“This cannot happen,” said Ayman Nour, a former presidential hopeful who quit the constitutional assembly this year. “It would be the biggest treason in Egypt’s history.”

Others are interpreting the vote as a way to quickly defuse anger about Morsy’s recent decree granting himself expanded presidential powers. The move sparked widespread protests, with demonstrators calling for Morsy to rescind the edict or resign.

If the council passes the draft, it will go before Egyptians for a popular vote within 15 days. If it passes in that referendum, the president’s controversial decrees will be lifted.

“This could be a way for him to get out of this debacle without reversing his decree and decisions,” said Aly Hassan, a judicial analyst affiliated with the Ministry of Justice.

The Constituent Assembly, formed to write the new constitution after the 2010 uprising that pushed former strongman Hosni Mubarak from power, originally had 100 members. However, several have walked out protesting previous decisions and Thursday’s surprise vote.

After the committee appointed 11 replacements — most of them members of the Muslim Brotherhood or Salafist Nour Party — it opened Thursday’s session with 85 representatives.

Senior Morsy adviser Essam El-Erian said earlier that despite the walkouts, remaining members would take their concerns into consideration when voting Thursday.

“Their brains and (all) their opinions are in the draft,” he told CNN’s Christiane Amanpour. He denied the process was being rushed, saying the assembly had been at work for six months.

The council’s work was taking place amid continued protests over Morsy’s decree last week that his decisions could not be overturned by judges, many of whom are holdovers from the Mubarak era and whom he has previously battled.

Clashes between rowdy protesters and police clogged streets in central Cairo Thursday and caused the closure of the U.S. Embassy nearby.

The embassy was not a target of the mayhem, but it issued a statement advising U.S. citizens to avoid the neighborhood, which is close to Tahrir Square, the epicenter of the current demonstrations and the Arab Spring protests that felled Mubarak.

The latest clashes follow two days of massive and sometimes violent protests against Morsy in cities across Egypt Tuesday and violence Wednesday between stone-throwing protesters and police who fired back with tear gas. The Tuesday protests were some of the biggest since Mubarak’s ouster in 2011. One man died in those protests, officials said.

Officers made arrests, beating some detainees.

Morsy and his backers described last week’s decree as an attempt to preserve the fragile Arab Spring revolution that pushed Mubarak from power and led to the country’s first free elections. But critics have called it an unprecedented power grab, and a Monday night statement declaring that the edict applied only to “sovereign matters” did nothing to defuse protesters’ anger.

Brookings Institution analyst H. A. Hellyer said the sudden push to approve the constitution could be an attempt to take some of the heat off of Morsy, Egypt’s first freely elected leader. Hellyer, who is currently in Cairo, considers that Morsy has “put himself in a tricky position” by issuing the edict because it has made it very difficult for him to compromise.

“I think his advisers are figuring out a way where he can climb down a little bit to defuse the situation without coming across as weak,” he said.

Despite critics’ concerns about its drafting, the constitution would probably pass in a referendum because many Egyptians crave stability after months of uncertainty, he said. Islamist groups may also cast the decision in a religious light.

But Hellyer said the huge numbers that turned out Tuesday — a workday — show that significant numbers of Egyptians from all backgrounds are unhappy about the president’s assumption of new powers.

“If the protesters can keep up the momentum for another couple of days, they hit Friday, a day off. If they can do something quite intense on Friday, then that may push the presidency in an awkward position,” Hellyer said.

It is also unclear whether Morsy would then give up his additional powers immediately, or whether he will keep hold of them until a parliament is formed, he said.

The Muslim Brotherhood has attempted to rally support for Morsy during the row. It dismissed Tuesday’s protests and plans nationwide demonstrations Saturday in support of the president and his decree, spokesman Mahmoud Ghozlan said Wednesday. The Brotherhood called off a planned “million man” protest Monday amid concerns about potential violence.

Meanwhile, Egypt’s judges have responded to the decrees by shutting down courts around the country. All but seven of Egypt’s 34 courts and 90% of its prosecutors went on strike Monday in protest, said Judge Mohamed al Zind of the Egyptian Judge’s Club. He described Morsy’s edict as “the most vicious … attack on the judicial authority’s independence.”

Analysis: Morsy makes his move

—CNN’s Reza Sayah and journalists Ian Lee and Mohamed Fadel Fahmy in Cairo, Michael Pearson and Ben Brumfield in Atlanta and Laura Smith-Spark in London contributed to this report.