Egypt’s ruling military council has set a 48-hour deadline for political parties to finalize the formation of a 100-member panel to write a new constitution, or it will draw up its own blueprint.

Lawmaker Mustafa Bakri on Tuesday outlined the ultimatum after representatives of 18 parties and independent lawmakers met with the head of the council, Field Marshal Hussein Tantawi.

The process has been deadlocked since the Islamist-dominated parliament tried to stack the body with its own people, leading to a walkout by secular and liberal members and the disbanding of the panel by a court order.

The dispute mirrors the splits in Egypt, two weeks before a presidential election runoff between a Muslim Brotherhood member and the last prime minister to serve the ousted President Hosni Mubarak the two most polarizing candidates.

It also highlighted the contentious role of the ruling military in post-Mubarak Egypt. The military rulers have drawn stiff criticism for their handling of the transition. They pledged to turn power back to a civilian government once a new president is in place, but there are some hints that they might try to hold back at the last moment if the outcome of the election is not in their favour, possibly using lack of a new constitution as a reason.

Several parties boycotted the Tuesday meeting, including the Brotherhood, the country’s most influential political group. Saad el-Katatni of the Brotherhood, who is the speaker of the parliament, lashed out at the military council. “No one can strip the parliament of its authority to issue legislation or laws,” he said.

Mr. Bakri said that if parties failed to name an assembly, the military council will issue “a supplementary constitutional declaration” to lay the blueprints for the panel.

Yasser Ali, a spokesman for Muslim Brotherhood candidate Mohammed Morsi, said if the military council went ahead with its declaration, “it will be hijacking legislative authority from parliament.”

“We won’t recognize whatever comes from the military council. This is our position,” he said.

The conflict over the constitutional panel adds tension to an already charged political scene, coming three days after Mubarak was given a life sentence for failing to stop the killing of protesters during last year’s uprising. Many uprising stalwarts demanded a death sentence.

Since the sentencing Saturday, angry Egyptians have swept into the streets, demanding justice and denouncing the whole election process.

On Tuesday, tens of thousands of protesters converged from several mosques around Cairo on Tahrir Square, the focal point of the uprising. A long banner read- “In the name of the martyrs’ blood, there will be a new revolution.”

Protesters demanded enforcement of “isolation law” that prevents Mubarak-era officials from contesting elections. The law, passed by parliament but still awaiting a ruling by Egypt’s Constitutional Court, might lead to a cancellation of the election. Others demanded formation of “civilian presidential council” to take over from the military.

Mr. Morsi is labelling himself as “the candidate of the revolution” and is trying to rally voters from among revolutionary and liberal groups to confront his rival candidate, Ahmed Shafiq, as Morsi tried to capitalize on the fear by many Egyptians that Shafiq would recreate Mubarak’s repressive regime.

Analysts believe if an Islamist is elected, the Brotherhood will not press to change Egypt’s political system from presidential to parliamentary a change that would give the Islamist-led parliament greater powers. If its candidate is defeated, then the Brotherhood would push to change the system to favour the parliament.

Many liberals blame the ruling council for not initially setting out clear standards for the panel in the country’s interim constitution, passed last year after the military council froze the old constitution.

“This is the trap the ruling council has put us in. Now it has to correct its mistakes,” said Ahmed Khairi, spokesman of Free Egyptians party.