Morocco on Thursday freed a young rapper who has emerged as one of the monarchy's most outspoken critics and who promptly denounced "thieves" and "scum" as he left prison.

The 24-year-old Mouad Belghouat, nicknamed "Al-Haqed" (the Vengeful One, in Arabic), served four months in a Casablanca prison for assault but was acquitted of another charge and released.

Belghouat, a member of the February 20 protest movement, was arrested in September after a brawl with a monarchist on charges his lawyers say were trumped up to silence a growing protest movement.

"There will be not turning back. Power to the people. Thanks to rap, I have committed myself for the people and its hardships. Our demands are huge," the defiant rapper told AFP on his release.

"We need a new deal, there is too much injustice. They brought in a new government but thieves are still enjoying impunity. We need to get rid of that scum," he said.

The Arab Spring wave of pro-democracy protests that felled Tunisia's long-standing dictator Zine el Abidine Ben Ali, Egypt's Hosni Mubarak and Libya's Moamer Kadhafi also inspired an unprecedented protest movement in Morocco a year ago.

King Mohamed VI offered significant reforms curbing his near absolute powers in a bid to pre-empt full contagion and called early polls that brought in a moderate Islamist party.