CAIRO—Egypt´s ruling military tightened its grasp on power even as the country´s top Islamist party contended its candidate won the presidency, in a fractious and sparsely attended vote that represented the country´s first democratic contest for the post.

There were no official poll returns, but the Muslim Brotherhood claimed that its count showed that Mohammed Morsi edged out the candidate identified with the ousted regime.

After the polls closed earlier Sunday evening, Egypt´s interim military rulers announced a constitutional declaration that expanded their power over civilian politicians and the drafting of a new constitution that is expected to take place in the next few months.

The move extends the military´s hold on legislative power and hems in the president to a role largely subject to the military leadership, the Supreme Council of the Armed Forces, or SCAF.

The constitutional declaration, together with orders issued earlier this week, raised new doubts about the military´s promise to hand over power to an elected president. It comes only days after the country´s high court ruled to dissolve Egypt´s democratically elected parliament and broadened its powers to search and arrest civilians.

The SCAF´s decision to extend its authority just as the polls closed appeared to be a thinly veiled assault on Islamist political forces. The Muslim Brotherhood has emerged as the primary check on the military´s dominance and Mr. Morsi was the top vote-getter in the first round of the presidential election in May.

The move extends the military´s hold on legislative power and hems in the president to a role largely subject to the military leadership, the Supreme Council of the Armed Forces, or SCAF.

The constitutional declaration, together with orders issued earlier this week, raised new doubts about the military´s promise to hand over power to an elected president. It comes only days after the country´s high court ruled to dissolve Egypt´s democratically elected parliament and broadened its powers to search and arrest civilians.

The SCAF´s decision to extend its authority just as the polls closed appeared to be a thinly veiled assault on Islamist political forces. The Muslim Brotherhood has emerged as the primary check on the military´s dominance and Mr. Morsi was the top vote-getter in the first round of the presidential election in May.

Mr. Morsi is running against Ahmed Shafiq, a former air force general who former President Hosni Mubarak appointed as prime minister just days before stepping down in the face of massive protests last year.

Mr. Shafiq´s campaign held a news conference Sunday night to complain about what it said were voting irregularities committed by Muslim Brotherhood supporters.

The election commission said official results were expected by the end of the week.

At a predawn Monday news conference at Mr. Morsi´s campaign headquarters, meanwhile, a spokesman for the Brotherhood´s Freedom and Justice Party said its candidate had won the presidency, according to their nationwide tally of votes. Mr. Morsi had 52.5 % of the vote versus Mr. Shafiq´s 47.5%, with nearly 98% of polling stations counted, the spokesman said.

The announcement provoked chants of "Revolutionaries, free, will complete the journey," and "down with military rule" among the gathered supporters.

Speaking soon afterwards, Mr. Morsi said the revolution had put Egypt on the "road to democracy" and offered his respects to those who died in the uprising. He didn´t comment on the military´s declaration earlier.

"We are not interested in revenge or settling scores," Mr. Morsi said. "We all want stability and look forward to a civil, modern state based on a constitution"

The military´s announcement sent shock waves through Egypt´s political class, magnifying the shock many Egyptian activists and Brotherhood supporters already felt over the dissolution of parliament last week.

Egypt´s military appeared to set itself up for a confrontation with the civilian politicians it had once invited to participate in the country´s chaotic transition to democratic rule. Its declaration immediately elicited a harsh response from civilian politicians across the political spectrum.

Mahmoud Ghozlan, a Brotherhood spokesman, which had enjoyed a plurality in the now-defunct parliament, said the declaration was "far worse than we expected" and called it a "violation of all constitutional and patriotic principles."

Brotherhood leaders had insisted all week the parliament disbanding was illegal, as was the soldiers´ move to seal off the parliament building last week.

Abdel Moneim Aboul Fotouh, a former reformist leader in the Brotherhood who failed to finish among the top two vote getters in the first round of the presidential poll, called the declaration a "complete military coup," echoing his criticism of the SCAF earlier in the week.

The announcement completely strips the Brotherhood of its most sought- after prize: the right to draft Egypt´s new constitution, a process that was earlier to have been dominated by a Brotherhood-laden parliament.

The declaration awards the SCAF the exclusive right to select delegates to a constitutional drafting committee and gives the Supreme Constitutional Court—the same judicial body that last Thursday dissolved parliament—effective veto power over the disputed issues in the drafting process.

The military´s announcement also places severe limits on the incoming president´s powers to declare war and exercise authority over the budget.

"The constitutional declaration means that whoever the next president is, he is meaningless," said Ahmed Said, the head of the liberal- minded Free Egyptians Party.

In an email to reporters on Sunday evening, the SCAF announced that it would hold a news conference on Monday morning.

Some secular-minded politicians who had long opposed the Islamists´ brash political ambitions cast blame on the group.

"All of the blame should be placed on the majority in the parliament that gave SCAF an opportunity to issue this constitutional declaration that they couldn´t have issued before," said Basel Adl, a leader in the secular-minded Free Egyptians Party. "The Brotherhood´s actions made this possible."

Some analysts compared Sunday evening´s constitutional declaration to the Turkish military coup of 1980 that paved the way for two decades of effective military rule in that country, said Omar Ashour, head of the Middle East Studies Program at the University of Exeter in the United Kingdom.

Michael Hanna, an Egypt expert with the New York-based Century Foundation, said the document effectively nulls the 16-month military- led transition to democracy.

"It´s a ceremonial transition," he said. "There is no transition, in fact."

—Saleh El Ghamrawi contributed to this article. (Copyright © Dow Jones & Company, Inc.) 06/18/12)