Rabat Human Rights Watch called on Morocco Wednesday to free a young rapper critical of the monarchy and quash the case against him for a song denouncing the police.

Mouad Belghouat, one of the country's most famous rappers, was arrested three weeks ago and is now awaiting his next appearance in a Casablanca court on April 25 for a charge of insulting public officials.

"This matter is simply a matter of freedom of expression," the New York-based rights group said. "Every day he spends in prison is a reminder of the distance between Morocco's laws and its practice, as well as the rights guaranteed by its new constitution."

The charge against Belghouat stems from a YouTube video of one of his songs, which includes images of Moroccan police officers. Human Rights Watch said Belghouat "denies any link with this video."