Faced with the prospect of being ruled by an all-powerful military fronted by a president with deep ties to the ousted regime of Hosni Mubarak, Egypt's secular pro-revolution political forces have struck a tenuous alliance with the Muslim Brotherhood in one final push to wrest back the momentum of the transition. 

In a press conference on Friday to announce the pact, Brotherhood presidential candidate Mohammed Morsi said the new front of ideologically opposed parties "represents the unity of all political forces and affiliations in Egypt". 

"We have held two consecutive meetings, and the discussion was rich and comprehensive, and we all agreed on the supreme goals of the revolution," he said. 

The announcement came amid an increasingly heated showdown between the Brotherhood and the ruling Supreme Council of the Armed Forces [SCAF], who are engaged in a high-stakes test of wills to decide the balance of power in post-Mubarak Egypt. The Brotherhood believes Morsi defeated rival Ahmed Shafik, Mubarak's last prime minister, in the runoff election that ended on Sunday, but it fears the SCAF will find a way to invalidate the results and give Shafik the victory when official results are announced in the coming days. 

That looming possibility has apparently motivated Egypt's pro-revolution groups to throw in their lot with the Brotherhood to stop the rise of what they see as a greater evil – the SCAF. But there were signs the coalition would not last. 

Watching from the crowd as his father, the prominent Brotherhood MP Mohamed el-Beltagy, appeared alongside Morsi, Omar el-Beltagy expressed his doubts.

"Yesterday I attended the same meeting for this group, and they were talking about, 'We cannot continue with the Muslim Brotherhood,'" he said. "The only thing that gives us unity is to resist the old regime and Ahmed Shafik." 

Beltagy said the new alliance was powerful but predicted the non-Islamists would soon be competing with the Brotherhood again, especially when the time comes for new parliamentary elections, perhaps as soon as later this year.

The two currents have grown apart since the 2011 uprising, when they fought side by side in the momentous street battles where the protests' survival was decided. Liberals, leftists and secularists accuse the Brotherhood of selling them out to the military for political power, while the Brotherhood has scorned the so-called "revolutionary youth" for bumbling and arguing their way through the transition with no real political plan. 

Shadi al-Ghazali Harb, a member of the Revolutionary Youth Coalition whose Awareness Party failed to gain a seat in parliamentary elections, said both sides needed one another in the fight against the military and that liberals and secularists should not be pleased with undemocratic setbacks for the Brotherhood, such as the court-ordered dissolution of the Brotherhood-dominated parliament earlier this month, which was seen as being welcomed by the SCAF. 

On Friday, Harb stood next to Morsi as he announced the pact. After the press conference, he explained his decision. 

"I can promise if they isolate themselves again, they lose [our trust] forever, this is their last chance," he said. 

While Morsi was not made to sign any written declarations during the marathon meetings, Harb said he and others demanded that Morsi publicly promise that his vice president would not be a member of the Brotherhood. 

"These elections have shown that the Muslim Brotherhood needs us," Harb said, pointing to Morsi's apparently 900,000-vote lead over Shafik, based on the Morsi campaign's results. Voters who sided with pro-revolution candidates in the first round were the ones who put Morsi over the top in the second, Harb claimed. 

Harb said the secular groups negotiated with Morsi and high-ranking MPs Mohammed el-Beltagy and Osama Yassin from the Brotherhood's Freedom and Justice Party but refused to include Khairat el-Shater, perceived by many as the top decision-maker in the Brotherhood, since he was not an elected official. 

Though Mohamed ElBaradei, the independent torchbearer for Egypt's secular progressives, has endorsed the coalition, notably absent at the Friday press conference were the non-Islamist groups that actually won the most seats in parliament – the Free Egyptians and Social Democratic Party. 

Both groups are seen as being staunchly opposed to the Brotherhood and insistent on enshrining Egypt's government as civil, not religious.

"They're not as kind of revolutionary as these guys," Harb said. "They're very much pro having a civil state … so if it's the SCAF that could bring a civil state I think for them it's OK." 

For Ahmed Maher, the well-known head of the pro-democracy April 6th Movement, who has also put his organisation behind Morsi, the choice amounted toward supporting malleable extremists over an armed dictaroship. 

"The Muslim Brotherhood is not like the military, the Brotherhood doesn't have weapons, it doesn't have tanks," he said. "They might be radical, but they're like a political party."