Morocco's king has ordered an investigation after his pardoning of a Spanish paedophile sparked violent protests in the country.

In a statement late on Saturday, King Mohamed VI said he ordered "that a deep investigation be conducted in order to determine responsibilities and loopholes that might have entailed this regrettable release, identify the one or those responsible for this neglect and take the needed sanctions."

The paedophile was sentenced in September 2011 to a 30-year jail term after being convicted by criminal courts in Kenitra, near Rabat, of raping 11 children.

He was among the 48 jailed Spaniards who were pardoned by King Mohamed VI on Tuesday at the request of Spain's King Juan Carlos, who visited Morocco last month.

But the release outraged the Moroccan society late on Friday, as protests erupted in many cities across the country demanding the royal pardon be revoked and the Spaniard be brought back to jail.

"It is evident that the Sovereign would never have consented that Daniel Galvan Fina would cease serving his sentence, given the atrocity of the hideous crimes of which he was found guilty," state-run news agency MAP said late Saturday.