CAIRO — The Muslim Brotherhood said on Friday its candidate — Mohammed Morsi — had a slight lead in Egypt's first free presidential vote and had won the right to engage in a run-off election next month, probably against former air force chief Ahmed Shafiq, who was deposed leader Hosni Mubarak's last prime minister.

This week's first-round vote has polarized Egyptians between those determined to avoid handing the presidency back to a man from Mubarak's era and those fearing an Islamist monopoly of ruling institutions. The run-off is planned for June 16 and 17.

The election marks a crucial step in a messy and often bloody transition to democracy, overseen by a military council that has pledged to hand power to a new president by July 1.

The second round threatens further turbulence. Opponents of Shafiq have vowed to take to the streets if he is elected.

But to supporters, Shafiq's military background offers reassurance that he can restore order on the streets, a major demand of the population 15 months after Mubarak's ouster.

A Shafiq presidency would also mean smoother relations between the head of state and the powerful military.

"It is clear that the run-off will be between [the Brotherhood's] Mohamed Morsi and Ahmed Shafiq," a Brotherhood election official, who asked not to be named, told Reuters.

The Brotherhood's Guidance Office, its top body, was meeting to mull a campaign "to galvanize Islamists and Egyptian voters to face the bloc of the 'feloul'," he said, using a scornful Arabic term for "remnants" of Mubarak's order.

Official results are not due to be announced until next week, but representatives of the candidates are allowed to watch the count, enabling them to compile their own tally.

The Brotherhood official said that with votes counted from about 12,800 of the roughly 13,100 polling stations, Morsi had 25 percent, Shafiq 23 percent, a rival Islamist Abdel Moneim Abol Fotouh 20 percent, and leftist Hamdeen Sabahy 19 percent.

No comments from any of the dozen candidates or state election officials were immediately available.

Election committee officials had said late on Thursday as counting began that turnout was about 50 percent of Egypt's 50 million eligible voters. The Brotherhood official, however, said about 20 million votes were cast, or about 40 percent.

EGYPTIANS FRET

The Brotherhood, Egypt's most organized political group, has already secured the biggest bloc for its party in parliament after an earlier vote. Long repressed and banned under Mubarak, the 84-year-old Islamist group has a broad grass-roots base.

Many Egyptians, including those who saw the revolt against Mubarak as a matter of national pride not religion, fret about Islamist gains since his fall. Christians, who form a tenth of the population and who already complain of discrimination, worry that Islamists in power could marginalize them further.

"We are confident that the next president of Egypt is Mohamed Morsi," said Essam el-Erian, a senior official in the Muslim Brotherhood's party, said after early counting.

If Mursi becomes president, Islamists will control most ruling institutions — but not the military — in Egypt, the most populous Arab nation, consolidating electoral gains made by fellow-Islamists in other Arab countries in the past year.

The powers of Egypt's next president remain undefined because of a tussle over who will write the new Constitution. He could be restricted by generals determined to retain their privileges and influence, even after the promised handover.

First-round voting was held in a calm atmosphere over two days with polls closing late on Thursday. Monitors did not report any major infringements that would invalidate the vote, although some candidates grumbled about their rivals' conduct.

A page on Facebook, a medium used to devastating effect in the revolt against Mubarak, was launched on Thursday and threatened a "revolution" if Shafiq or another former minister under Mubarak, Amr Moussa, was elected.