RABAT, Morocco (AP) — Moroccan demonstrators frustrated over inequality and corruption are defying a police ban and holding a protest in a northern city that has become a symbol of mounting public anger.

Moroccans from other cities and abroad expressed their support on social networks for the protesters who gathered Thursday in El Hoceima, amid a reported heavy police presence.

Their Hirak protest movement has become the biggest challenge to the kingdom, a key U.S. ally known for its stability, since the Arab Spring in 2011.

Movement leader Nasser Zefzafi called for a protest July 20 before his arrest last month following a dramatic manhunt. Authorities banned Thursday's demonstration for administrative reasons.

Protesters are demanding government investment in the impoverished northern Rif region, and justice for a fish vendor crushed by a garbage compactor.