Demonstrators lift placards and chant slogans during a youth-led protest demanding reforms to public healthcare and education at Mohamed V square in Casablanca. AFP
The open letter -- signed by academics, artists and human rights defenders -- backed the demonstrations and came ahead of the king's annual speech on Friday.
"We are addressing you because you hold the ultimate authority and ultimate responsibility in this country," the signatories wrote, urging the monarch to "act in depth".
"The people of Morocco are suffering, and its youth are shouting about it in the streets."
The protests erupted in late September with calls for reforms to public education and healthcare, after eight pregnant women died at a public hospital.
Since then, demonstrators have also demanded an end to corruption and the resignation of Prime Minister Aziz Akhannouch.
The protest movement, GenZ 212, is a newly formed collective based on the Discord web platform whose founders remain unknown.
Earlier this week, the group said it was suspending demonstrations to prepare a bigger rally on Thursday, ahead of the king's speech.
On Wednesday, the group said it would not hold protests on the day of the speech "out of respect" for the monarch, stressing that this "does not mean backing down from our demands".
The letter described the protesters' demands as "legitimate" and urged the king to launch constitutional reform and an "effective fight against corruption".
"What's really necessary is to address the deep, structural causes of the anger that is shaking our country," it said, also calling for the release of recently detained protesters and prisoners of conscience.
Many Moroccans have expressed frustration over public spending priorities as the kingdom pushes ahead with major infrastructure projects in preparation for the 2030 World Cup, which it will co-host with Portugal and Spain.
The state's priorities "should be focused on the basic needs of the people... instead of persisting in lavish spending such as the largest football stadium in the world", the letter said.
Akhannouch, whose tenure ends next year, has said his government was willing to engage in dialogue and respond to the protesters' demands, but calls for his resignation have persisted.
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