RABAT - Thousands of Moroccans led by an Islamist movement rallied in the capital Rabat on Sunday in a massive show of support for protests against corruption and official abuses in a northern region that have tested authorities for weeks.Chanting against "ruling mafia" and carrying portraits of detained activists, protesters packed Rabat's Bab El Hed area and marched toward the parliament, with most from the Adl Wal Ihsan (Justice and Spirituality) Islamist movement.Political unrest is rare in the North African kingdom but protests around northern city Al-Hoceima since October have been the largest since the 2011 "Arab Spring"-inspired rallies that prompted the king to cede some powers.The participation of Justice and Spirituality is significant. A major player in the 2011 protests, the movement is banned from formal politics, but is the only opposition group able to mobilize on a massive scale."We came out to protest about the social reality in Morocco," said Lamia, a school teacher who came from the northern city of Tetouan to the Rabat rally. "We're here in solidarity with Al-Hoceima, to demand dignity."Police estimated the rally was more than 10,000 strong, though Justice and Spirituality said it was much larger. It was the most significant political rally in Rabat since the 2011 unrest and smaller leftist groups and labour unions, as well as some parliamentary opposition parties, also participated.Some chanted slogans, including: "You're corruption is starting to stink."The northern protests erupted in October in Al-Hoceima after fishmonger Mouhcine Fikri was crushed inside a garbage truck while trying to salvage his fish that had been confiscated by police.Fikri's death has become a symbol for frustrations about official abuses and revived the spirit of the February 20 movement that led pro-democracy rallies in 2011 and prompted King Mohammed VI to carry out constitutional reforms.Some of the anger in the Al-Hoceima protests has been directed at "Makhzen", the royal governing establishment, but the unrest has not been aimed at the king. Morocco has a deeply rooted monarchy, the Muslim world's longest-serving dynasty.But tensions in Al-Hoceima and the Rif region, long a hotbed of anti-government dissent, have been rising since the arrest of the protest movement's leader Nasser Zefzafi on charges of threatening national security.The unrest is testing nerves in a kingdom that presents itself as a model for stability and gradual reform, as well as a safe haven for foreign investment in a region affected by militant violence.