RABAT: Tens of thousands of Moroccans took part in the funeral of the leader of the North African state's biggest opposition group on Friday, in a sign of the huge support commanded by Islamists opposed to the monarchy.

Sheikh Abdessalam Yassine, who formed al-Adl Wal Ihsane (Justice and Spirituality) in 1981, died on Thursday at the age of 84 after suffering from influenza.

The group is banned from formal politics but believed by analysts and diplomats to be the only opposition organisation capable of mass mobilisation against the monarchy.

Security forces circled the mosque where the Friday prayers were held in downtown Rabat and prevented the mourners from passing through the main street of the capital.

No members of the government or the royal palace attended, although local media had speculated Islamist Prime Minister Abdelilah Benkirane would go.

King Mohammed allowed Benkirane to form a government last year after his PJD party won early elections - part of royal efforts to calm large-scale protests for democratic reforms following uprisings in Egypt and Tunisia that removed entrenched autocratic rulers.

The king also enacted constitutional reforms that limited some of his powers, though critics say the king and his advisers, not the elected government, remain the real source of power.

Official media ignored the death and the funeral. The government is wary of a return of mass protests as it faces economic difficulties from the effects of the euro zone crisis and increased social spending last year to quieten the protests.

"In Al-Adl Wal Ihsane we are like family. We came with my husband and our neighbours to say goodbye to our teacher and our leader," said Lamia El Hassnaoui, a student member of the movement near the mosque.

"I'm not afraid or worried about our group's future - he left behind him an organisation with democratic institutions behind him."

Diplomats and analysts say there is no clear successor to Yassine and that his group could face internal dispute over whether to try to enter official politics - a move that would require it to tone down its opposition to a king who styles himself "Commander of the Faithful".

Yassine, who hailed from a Berber village in the south of Morocco and grew up in Marrakech, had a history of challenge to the authorities that often landed him in jail.

He was imprisoned for three years after he addressed a letter to King Hassan in the 1974 calling for implementation of sharia, or Islamic law.

He was held for two years again after forming his political group and spending 10 years under house arrest until King Hassan's son succeeded him in 1999.

He called on the new king too to turn to the "true Islam" and surrender the monarchy's assets to the state but while the authorities left him alone, his party remained banned.