Sultan Qaboos, Oman's ruler, has pardoned all dissidents jailed for defaming the leader or taking part in protests, state news agency ONA has said.

The agency did not say how many prisoners were expected to be freed, but activists say courts had sentenced at least 50 dissidents to jail terms of up to 18 months last year.

"His Majesty Sultan Qaboos has issued a royal pardon for those convicted of defamation, information technology crimes and unauthorised rallies," the agency said.

Amnesty International, the international human rights group, welcomed the move.

"However, individuals peacefully exercising their right to freedom of expression should never have been put in prison in the first place, nor tried on charges that criminalise freedom of expression," it said in a statement received by the Reuters news agency.

Last week a court freed on bail eight activists, part of a group of prisoners who went on hunger strike last month saying they had been sentenced unfairly. The court ordered a re-trial.

The government has recently sought to ease public discontent by announcing plans to limit the number of foreign workers and sharply raise the minimum wage for locals in a drive to increase employment of Omani citizens.

Oman, which sits on the Strait of Hormuz through which some 40 percent of the world's sea-borne oil exports passes, has also pledged to create tens of thousands of public sector jobs.