The Rif has been shaken by social unrest since the death in October of fishmonger Mouhcine Fikri, 31, who was crushed in a rubbish truck as he protested against the seizure of swordfish caught out of season.
Initial protests in the fishing port of Al-Hoceima triggered a wider movement demanding more development and railing against corruption, repression and unemployment.
Nasser Zefzafi, who emerged as the head of the grassroots Al-Hirak al-Shaabi, or "Popular Movement", was arrested on Monday after three days on the run.
Late Wednesday, between 2,000 and 3,000 protesters once again took to the streets of Al-Hoceima, shouting slogans such as "We are all Nasser Zefzafi" and "Corrupt state".
"Arrest us, we are all activists," read one banner.
Although fewer demonstrators turned out than the previous night, the protest appeared better organised, with volunteers in fluorescent jackets including women marshalling the crowd.
The mainly ethnically Berber Rif region has long had a tense relationship with Morocco's central authorities, and was at the heart of Arab Spring-inspired protests in 2011.
Cilia Hirani, a member of the Popular Movement, told AFP that everyone in the Rif "believes in freedom, in humanity and in social justice".
"If you imprison our leaders, we will resist and we will resist until our demands, which are rights in democratic countries, are granted," she said.
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Najib Ahamjik, often referred to as the movement's number two, remains at large but continues to use social media to call for "mobilisation".
Nawal Benaissa, one of the public faces of the Popular Movement, was among three young women on Wednesday who urged protesters to demand "freedom for prisoners".
- 'Stay peaceful' -
On Thursday morning, she said she was called in to the police station in Al-Hoceima, and was seen leaving the building again a short time later.
Anti-riot police were present at Wednesday's protest, following clashes between demonstrators and security forces over the weekend, but the crowd dispersed at around midnight without incident.
Zefzafi was detained along with others on Monday for "attacking internal security", after a warrant for his arrest issued Friday sparked turmoil in Al-Hoceima, a city of 56,000 inhabitants.
A new video of Zefzafi has been posted on social networks, apparently recorded shortly before his arrest, in which he says: "My brothers, the moment is very sensitive... Stay peaceful, above all."
State media and politicians have remained largely silent about the events, but the local branches of three parties including the ruling Justice and Development Party (PJD) issued a joint statement warning of a "serious situation" and criticising the response of the authorities.
Out of around 40 people reported arrested on Friday, including core members of Al-Hirak, 25 have been referred to the prosecution.
Their trial began Tuesday but was pushed back to June 6 at the request of their lawyers, who have complained their clients were ill-treated during their detention.
Seven suspects were released on bail and another seven were freed without charge.