Andre Pain/European Pressphoto Agency
Supporters of Mohamed Morsi, the Muslim Brotherhood’s presidential candidate, protest against the military's tightening grasp on political power in Tahrir Square.

CAIRO — Egypt’s military rulers warned on Friday that they would use “the utmost firmness” against anyone they deem to threaten “the higher interests of the country” just as tens of thousands of demonstrators flooded into Tahrir Square here for the fourth day of demonstrations against the dissolution of Parliament and reassertion of their power.

“The Armed Forces have emphasized self-control out of respect for the revolutionary state to avoid losses or injuries as part of the people exercise their right to express their opinions,” a spokesman for the ruling military council declared in a statement, suggesting the military’s patience was nearing an end. “Everyone should respect the principles of legitimacy for fear of the dangers of abandoning them.”
Alluding to a court decision the military used to justify the dissolution of Parliament, the military spokesman said: “The verdicts issued by the judiciary are enforced in the name of the people, and refraining from enforcing them or hindering their enforcement is a crime punishable by law.” The statement was broadcast on television just after Friday Prayer as crowds were streaming out of mosques and toward the square.
The statement appeared to be aimed primarily at the Muslim Brotherhood, the Islamist group that was the principal opposition to the military-backed autocracy under former President Hosni Mubarak. It was an escalation in the mounting conflict between the Brotherhood and the military council over the generals’ moves to tighten their grasp on political power just at the moment that they had vowed to relinquish it.
Many Egyptian and Western analysts have described their moves as a military coup, if not a counterrevolution. And it has triggered the most serious political crisis in the 16 tumultuous months since the ouster of Mr. Mubarak.
On the eve of last weekend’s presidential election — which the generals had promised would conclude their reign — the military instead dissolved the Brotherhood-led Parliament. And as the polls closed Sunday, the military council further decreed a new interim constitution granting itself broad legislative powers and a virtual veto over any permanent charter while stripping away most of the new president’s authority.
Having held its fire until the ballots were counted, the Brotherhood has claimed victory in the presidential race, citing a public vote count that was confirmed by state media and outside observers. And its leaders have vowed to respond with escalating street protests as well as legal challenges demanding that the military hand over power as promised, restoring the Brotherhood-led Parliament and recognizing the victory of its presidential candidate, Mohamed Morsi.
But the presidential election commission, a panel of judges appointed by Mr. Mubarak, has postponed confirmation of the official results, saying it needed more time to consider accusations of fraud or manipulation by both sides.
Mr. Morsi’s opponent, Ahmed Shafik, a former Air Force general and Mr. Mubarak’s last prime minister who campaigned as a new secular strongman, has also declared himself the winner. And the Brotherhood has charged that the delay in confirming the widely acknowledged results is a veiled threat by the military council to try to take away the presidency if the group does not back down from its challenge to the military.
In its statement Friday, the military council charged in a veiled stab at the Brotherhood that rushing out an announcement of the election results was causing division and damaging national unity. The council redoubled its commitment to its interim constitution, calling it “a necessity” because of the dissolution of Parliament.
And it defended its legal justification for shuttering the Parliament one week ago, a day after a hurried decision by a Mubarak-appointed constitutional court had found fault with a technical application of election rules for a third of its seats. In the past, similar challenges to the legitimacy of an elected Egyptian Parliament took three or four years to decide, and then resulted in a popular referendum on the legislature rather than an immediate military takeover.
The Brotherhood, the only political force that is seen as a potential counterweight to the military, has said repeatedly that it is seeking to establish an explicitly Islamic government as well as a multiparty constitutional democracy, the peaceful rotation of power and protections of minority rights.
But after more than six decades of political life defined by secular autocrats battling real and supposed Islamist militants, Egyptians are divided over their views of the group.
While the Brotherhood has led this week’s protests, some of the more secular minded leftist or liberal activists who helped prompt the revolt against Mr. Mubarak — notably the influential April 6 Youth Group — have also urged everyone to go to the streets. But many older secular politicians have appeared to support the military as a bulwark against an Islamist takeover.
Each day the standoff has grown increasingly tense. A few blocks from the swelling crowds in Tahrir, a contingent of soldiers and riot police continued to guard the Parliament building Friday to prevent any attempt by lawmakers or others to enter. Tanks, armored personnel carriers and other military forces have resumed positions a on the road into the city from Alexandria that they had occupied during the uprising against Mr. Mubarak.
On Thursday, Mohamed ElBaradei, the Nobel Prize winning United Nations diplomat who was among the only voices to forecast that revolt, called for some mediation between the military and the Brotherhood, warning that the situation could soon explode.