AMMAN, Jordan—After a pardon from the king, Jordan has released 18 activists arrested during a protest last month when they allegedly chanted against the country's monarch.

A Jordanian prosecutor said Thursday that two other men detained with the group remain in custody because they are not part of the youth activist movement. The prosecutor spoke on condition of anonymity because he is not authorized to talk to the media.

There have been several incidents recently with activists and media commentators charged with defaming King Abdullah II.

Human Rights Watch has repeatedly urged Jordan to abolish laws criminalizing peaceful free speech and assembly.

Under Jordan's current law, the state security court has jurisdiction over speech-related crimes, including insulting the king—a taboo punishable by up to three years in jail.