CAIRO — The head of the assembly drafting Egypt’s new constitution said the final draft should be finished on Wednesday, as the Islamist-dominated body races to finish a process that has helped to trigger a political crisis.

The constitution is a crucial element of Egypt’s transformation to a new system of government after last year’s overthrow of the autocratic president, Hosni Mubarak.

But it is also one of the reasons why President Mohamed Morsi is at loggerheads with his non-Islamist opponents, in particular over a decree he issued last Thursday that expanded his powers.

“We will start now and finish today, God willing,” Hossam El Gheriyani, the assembly speaker, said at the start of its latest session in Cairo.

“If you are upset by the decree, nothing will stop it except a new constitution issued immediately.”

Three other members of the assembly, which is being boycotted by most of its non-Islamist members, said there were plans to put the document to a vote on Thursday.

A Muslim Brotherhood official who declined to be named also said a quick conclusion of the constitutional process could offer a way out of the crisis, because the decree would be overridden by the new constitution.

He said Thursday would be a “great day”, without elaborating, and called on the members who had withdrawn from the body to return.

Gheriyani said members should come early to Thursday’s session, which would start at 10:00am.

Assembly members Younes Makhyoun and Salah Abdel Maboud, both Salafi Islamists, told Reuters a vote on the final draft was planned for Thursday. Amr Abdel Hadi, one of the few remaining liberal members, said the same.

“We will finish today and there is agreement on almost all articles... and then we will start voting,” Makhyoun said.

Leading opposition figure Amr Musa, who withdrew from the assembly last month, said it was misguided to conclude the process so fast.

“This is nonsensical and one of the steps that shouldn’t be taken, given the background of anger and resentment to the current constitutional assembly,” he told Reuters.

The assembly has been working since June to finish the document, supposed to be the cornerstone of Egypt’s new democracy. It will be put to a popular referendum once the assembly approves it.

Meanwhile, the Muslim Brotherhood and hardline Salafi parties will hold protests across Egypt on Saturday in support of Morsi, who is facing a wave of unrest over a decree that expanded his powers.

Mahmoud Ghozlan, the Brotherhood spokesman, told Reuters: “We have called for pro-Morsi nationwide protests. The exact locations of the protests are currently being discussed.”

Salah Abdel Maboud, a leading member of the Salafi Nour Party, confirmed Islamists would stage protests on Saturday. He said the location could be Tahrir Square, where Morsi’s opponents have been camped out for seven consecutive days.

But Nader Bakkar, the Nour Party’s spokesman, told Reuters both the Nour Party and its founder the Salafi Call would steer clear of Tahrir Square.

“We do not want to enter into conflict with anyone,” Bakkar said.

The Brotherhood, Egypt’s most organised and popular Islamist group, had previously cancelled its call for a big pro-Morsi rally last Tuesday because of fears of violence between the president’s supporters and opponents, who had also called for mass demonstrations on the same day.

Anti-Morsi protesters say they will stay in Tahrir Square until the decree is withdrawn, bringing fresh turmoil to a nation at the heart of the Arab Spring and delivering a new blow to an economy already on the ropes.

Egypt’s cassation and appeals courts said on Wednesday they would suspend their work until the constitutional court rules on the decree, which has further damaged Morsi’s already testy relationship with Egypt’s judges.