Egypt’s opposition Muslim Brotherhood held the government responsible on Sunday for attacks on protesters during last week’s referendum. Witnesses said supporters of President Hosni Mubarak’s ruling National Democratic Party beat, kicked and punched activists and journalists who were urging a boycott of a May 25 referendum on a new system for electing the president. The new system, approved in the referendum, opens the way for Egypt’s first multi-candidate presidential poll. But opponents say it will not allow a credible challenge to Mubarak, in power since 1981 and widely expected to seek a fifth term.

“Through its backing of the thugs and lack of intervention to stop the attacks on the demonstrators, the Interior Ministry is considered responsible for these immoral excesses,” the Muslim Brotherhood said in a statement. “It is necessary to hold accountable those responsible so as to serve as a lesson to those outside the law and constitution.” Egypt’s presidential spokesman said on Saturday the media had overplayed the attacks, but such incidents were still unacceptable. Public Prosecutor Maher Abdel Wahed is investigating complaints of violence.

Witnesses said female activists and journalists were molested and some had clothes ripped from them. “Paying gangs of paid thugs ... to attack and sexually harass female demonstrators and journalists is good proof of the present regime’s lack of intention or serious desire for reform,” the Brotherhood said.

Egypt has detained hundreds of members of the banned Muslim Brotherhood, probably Egypt’s biggest opposition group, as part of a crackdown in recent weeks after the group staged protests calling for reform. About 775 are still being held. In a separate statement, the Brotherhood said police had tortured Khairy Mohamed Omar, a political science researcher. It said he was stripped, beaten on his genitals and threatened with sexual attack.