By Zakia Abdennebi

RABAT (Reuters) - A Moroccan editor who rights activists say was unjustly prosecuted for criticizing the authorities walked free after completing his one-year jail sentence on Saturday and demanded an end to the practice of sending journalists to prison.

Rights group Amnesty International has described Rachid Nini as a "prisoner of conscience" and said he was punished for highlighting corruption and abuses by the kingdom's authorities, especially the security services.

Since Nini's arrest, pressure has been building for Morocco to stop using its criminal justice system to jail journalists over what they write, especially after the "Arab Spring" revolts improved media freedom in many parts of the region.

"I hope that I will be the last journalist to be imprisoned and tried under the criminal law," Nini told reporters and supporters who gathered at his home near Casablanca, Morocco's commercial capital, on Saturday.

"We want a press law to try journalists and not to be treated as criminals."

Nini was arrested in April last year. A court ruled he was guilty of crimes including "discrediting a court, trying to influence the judiciary and publishing information about untrue criminal offences".

It had been expected Nini would be released at 0730 GMT on Saturday from Casablanca's Oukacha prison. A crowd gathered outside to greet him. But rights activists said the authorities set him free about four hours earlier, when no one was there.

Morocco's new government, led by moderate Islamists who until late last year were in opposition, have said they will try to end old practices of jailing people unlawfully and abusing the rights of dissidents.

Rights activists say change is coming slowly. They point to the prosecution of a rapper over a song he posted on YouTube that was critical of the authorities. The rapper, known as El-Haqed, or "the Sullen One," is awaiting trial.

"We still have violations of freedom of expression and press freedom, this is still taking place in Morocco," Khadija Ryadi, chair of the Moroccan Human Rights Association, told Reuters.

(Writing by Christian Lowe; Editing by Maria Golovnina)