The outlawed Muslim Brotherhood captured at least 25 more seats in Egypt's parliament in a runoff vote Saturday, despite what appeared to be a determined government effort to block its supporters and slow the Islamic-based organization's building momentum.

Police fired tear gas at several polling places and used rubber bullets at one as residents arrived to cast ballots. In another, a human rights worker reported that police kept out Brotherhood supporters, lifting their cordon only when ruling party supporters showed up in buses at sunset.

President Hosni Mubarak unexpectedly canceled plans to attend a European Union-sponsored summit Sunday in Barcelona, Spain. His spokesman, Suleiman Awwad, said developments in the Arab world were behind the cancellation and denied election unrest was the cause.

The preliminary Interior Ministry figures released early Sunday showed the fundamentalist Brotherhood increasing its share in parliament to at least 72 seats, a more than fourfold jump over its representation in the outgoing parliament — with a third and final stage of voting still to go on Dec. 1 and another runoff likely six days after that.

The outcome, if it becomes final, would give the Brotherhood enough seats to nominate a presidential candidate in 2011 under new constitutional rules.

Despite the Brotherhood's impressive gains, the ruling National Democratic Party had claimed 122 seats going into the Saturday runoff and was certain to maintain control of the 454-member legislature. New results for the NDP were not available early Sunday since its block in parliament also consists of nominally independent members who vote in lockstep with the ruling party.

The vote is seen as a test of the U.S.-allied Mubarak's pledge to open the country's authoritarian political system, but the strong showing by the Brotherhood has been followed by violence, unrest and detentions.

Saturday's runoff was to decide 122 seats in nine provinces where no candidate got more than half the vote in the second round of voting Nov. 20.

Election monitors complained that security forces blocked thousands of the 10 million eligible voters from entering polling stations.

"Voters are being forcefully barred from entering the polling stations (and) many polling stations are empty," said Negad el-Borai, a monitor and human rights activist.

Interior Ministry spokesman Ibrahim Hammad said no polling centers were closed and denied that police were blocking voters.

Judge Hesham el-Bastawisy denounced the violence in an interview with the Arab satellite television channel Al-Arabiya.

"What we've been hearing since early morning about what is happening at polling stations indicates this is not an election. It's a battle," el-Bastawisy said.

Senior Muslim Brotherhood member Ali Abdel Fattah said police arrested 680 members and supporters nationwide on Saturday.

In Laqana, a Nile Delta town 105 miles north of Cairo, police blocked all voters from reaching the polls. Muslim Brotherhood candidate Khalad Saad Attayia hails from the village and was said to have near unanimous support.

Dozens of residents showed an Associated Press reporter wounds and bruises they said they were caused by rubber bullets fired by police. Authorities launched volleys of tear gas every few minutes.

As polls closed at 7 p.m. — after 11 hours in which none of the 7,500 registered voters had cast ballots — streets in the village were empty of vehicle traffic but crammed with angry townspeople.

In the Mediterranean port of Alexandria, Egypt's second-largest city, a U.S. human rights worker at one polling station also reported that police kept Brotherhood supporters from voting but lifted their cordon to ruling party supporters who showed up in buses at sunset.

At that point Brotherhood voters and other opposition supporters began hurling rocks at police, who opened fire with tear gas, the observer said, speaking on condition of anonymity because his organization would not let him give his name.

Witnesses in many parts of Alexandria said people were choking from the tear gas and trying to seal their apartments from it.

Poll monitors and human rights groups said the violence, coupled with wide-scale arrests, contributed to poor turnout across the country.

Egypt's elections began Nov. 9 and conclude Dec. 1, with a third-stage runoff likely six days later.

The first stage of voting was mainly peaceful, but violence and police interference increased dramatically after the Brotherhood's strong showing. At least one person died in violence in Nov. 20 voting; hundreds have been wounded in melees. Most credible reports blame security forces and the NDP.

The Muslim Brotherhood was banned in 1954 and later that year accused of trying to assassinate then-Interior Minister Gamal Abdel Nasser, who became president in 1956. It renounced violence in the 1970s and eludes the ban on its activities by fielding candidates as independents.

The Brotherhood's platform is based on a vague call for the implementation of Islamic law in the Arab world's largest nation. It advocates the veil for women and campaigns against perceived immorality in the media, but the group insists it represents a more moderate face of Islam than that followed in deeply conservative Saudi Arabia.