The prosecutor's office said the two, Eric Laurent and Catherine Graciet, remained in detention today.
Eric Dupont-Moretti, a lawyer for the king, told RTL radio yesterday that Laurent claimed he and Graciet were writing a compromising book about the monarch and demanded 3 million euros (USD 3.4 million) to keep it unpublished.
Dupont-Moretti said the Moroccan leadership filed a lawsuit in Paris and the arrests came after a sting operation.
The king has built a reputation as a moderate, modern leader, though journalists in Morocco have been jailed for criticizing him.