My money’s on the Islamists.

CAIRO (AP) – Muslim Brotherhood supporters and secular protesters hurled bottles and rocks at each other and got into fistfights in Cairo’s Tahrir Square on Friday as their political differences boiled over at a rally by tens of thousands marking an anniversary in the uprising that toppled Hosni Mubarak.

The scuffles, in which there were no reports of injury, were the first time the two sides have come to blows over resentments that have been rising between them since they worked together during the 18 days of protests against Mubarak a year ago.

Now they are locked in a competition to shape the transition. The differences do not focus on the Brotherhood’s religious agenda—though it worries many in the other camp. Instead, the divisions are over the military, which have ruled since Mubarak’s fall, and ultimately whether dramatic change will be brought to Egypt’s long autocratic system.

The “revolutionaries,” the leftist and secular activists who launched the anti-Mubarak revolt, now demand the ruling generals quit power immediately and have vowed protests to force them out. The Brotherhood, meanwhile, has vaulted to political domination by winning the largest bloc in the new parliament and has been willing to let the military follow its own timetable for stepping down.

The revolutionaries suspect the Brotherhood will strike a deal with the ruling generals—giving them a future say in politics to ensure the Brotherhood’s hold on authority and influence on the writing of a new constitution, effective shelving serious reform. They also bristle over what they see as the Brotherhood’s attempts to monopolize the political scene.

Nevertheless, the two sides have been uneasily trying to share Tahrir Square this week since a giant rally Wednesday marking the Jan. 25 start of the anti-Mubarak protests. But on a new rally Friday, tempers broke.

“Out, out, out!” revolutionaries chanted at the Brotherhood’s main stage in the square, holding their shoes in the air in a sign of contempt at a line of Brothers forming a human chain in front of the podium.

“Dogs of the military council,” others chanted at the Brothers.

The political differences have translated into a dispute over the very meaning of the anniversary. The Brotherhood has presented this week as a celebration of the revolution’s successes—particularly their own parliament victory. The secular groups say there is nothing to celebrate when so many demands of the revolution are left unachieved and killings of protesters have gone unpunished.

The fights erupted over the Brotherhood’s giant stage in the square, bristling with loudspeakers. Some protesters complain the Brotherhood sought to drown out other protesters by blaring religious anthems, Quranic recitations and music.

Others were angered a celebratory banner on the stage proclaiming, “Holiday of the Revolution.” Another note of triumphalism that irritated many was a song played repeatedly celebrating the military’s victories in the 1973 war with Israel and proclaiming “may the victory be bigger” in the revolution.