CAIRO, Egypt, AP – An Egyptian prosecutor has extended the detention of four leaders of the outlawed Muslim Brotherhood arrested in a government crackdown sparked by a wave of pro-reform protests by the banned Islamic movement.

The men face charges of belonging to a banned group, organizing unauthorized protests and inciting sedition. They were arrested May 6, when the group held nationwide protests to demand political reform. Their detention has been extended repeatedly and on Sunday was extended again for 15 days.

Emergency laws introduced in 1981 allow the state to hold suspects for six months without trial and allows authorities to re-arrest them indefinitely.

Essam El-Erian, a 52-year-old former lawmaker, spent five years jailed during the 1990s on charges of belonging to a banned group trying to change the regime in Egypt to an Islamic state.

Hundreds of Muslim Brotherhood members were arrested in May during a surge of protests by many groups in Egypt ahead of a historic referendum to amend the constitution and allow multi-candidate presidential elections for the first time.

The group says more than 300 of its members remain detained. The government said only 37 from those rounded up during protests remain in custody.

Human Rights Watch and an Egyptian human rights group have urged the government to free hundreds of political detainees, including Brotherhood members, being held without charges, some for years.

With presidential and parliament elections due later this year, Egypt has seen an unprecedented spate of protests calling for an end to the rule of President Hosni Mubarak, who is widely expected to run for a fifth term and win.

The Brotherhood, believed to be Egypt”s largest Islamist group, advocates an Islamic government but has renounced violence since the 1970s. Running as independents, Brotherhood members form the largest opposition bloc in the 454-member parliament, holding 15 seats.