The Egyptian state prosecutor on Wednesday ordered 147 detained members of the Muslim Brotherhood to be investigated on rioting accusations, a judicial official said, in the latest crackdown on the country's largest opposition group.

The detainees, who have not been formally charged, are also accused of holding unauthorized demonstrations after a flurry of protests in northern cities, said the official, who spoke on condition of anonymity because he was not authorized to speak to the media.

Thousands of Muslim Brotherhood members demonstrated across the Nile Delta on Tuesday, accusing the government of preventing them from participating in municipal elections set for April 8.

The demonstrators hurled stones at police, who responded by firing tear gas.

The 147 were detained Tuesday after the demonstrations, but the government did not announce accusations against them until Wednesday. The Brotherhood's Web site reported that the demonstrations were followed by dozens of arrests but did not give a total figure for those currently in custody.

Authorities have arrested more than 800 Brotherhood members over the past year as part of a stepped up campaign against the group. Several international human rights groups have criticized the detentions.

The Brotherhood has been banned in Egypt since 1954, but its members have won parliament seats by running as independents in elections. The group stunned the government by scoring large victories in the 2005 parliament elections, winning a fifth of the seats in the 454-member body.

The government then postponed 2006 municipal elections for two years, apparently out of fear of more Brotherhood gains.

Thousands of Brotherhood candidates have been prevented from registering for next week's elections for local councils, which have long been dominated by President Hosni Mubarak's ruling party.

The 4,500 local councils are responsible for services at a district, town and village level and are critical institutions in Egypt's centralized state control.