Morocco banned the February 16 edition of Spain's influential El Pais, as a cartoon published by the newspaper allegedly tarnished King Mohammed VI's name, an official said.
"The decision to ban (the paper) was made on the basis of article 29 of the press code" that protects the monarch, the senior communication ministry official told AFP on February 18.
"The caricature contains a deliberate intention to smear the (king's) image to harm the king personally," he added.
The cartoon, which was picked up by a Moroccan website, accompanied an article by Spanish journalist Ignacio Cembrero, who knows Morocco well.
Contacted by AFP, Cembrero said the Moroccan reaction surprised him as the small cartoon was "friendly and rather likeable".
The first ban since January
It seemed to be the first time that a foreign publication was banned for the stated reasons since the moderate Islamist Justice and Development Party (PJD) came to power in Morocco in January, he added.
So far Morocco has only banned weeklies that carried images of the Prophet Mohammed, or of God, which is forbidden under Muslim tradition.
Earlier this month French weekly Le Nouvel Observateur fell into that category after printing an image of God.
And last month the magazine was banned when a cover story on the Arab world included the supposed face of the Prophet Mohammed.
Morocco also banned French weekly l'Express in January for publishing a 95-page dossier on Islam including a face meant to represent the Prophet Mohammed's.
Cembrero was, along with El Pais's director, the last foreign journalist to interview the monarch in January 2005.
Early this week, Rabat's private economics school EGE cancelled a conference on Spanish-Moroccan relations where Cembrero was to speak on February 29, but did not give a reason.
Cembrero was in Rabat in late January during a visit to the country by Spanish Prime Minister Mariano Rajoy.
He wrote a book on sometimes tense relations between Madrid and Rabat, "Vecinos alejados", (Distant Neighbours) in 2006 and has attended public meetings in Morocco that also focussed on the latest upheaval in Arab countries.