An Omani court has jailed a prominent activist for three years for a range of offences including undermining the state, a charge reportedly related to an open letter to United States President Barack Obama about human rights in the country.

Lawyer Yaboub al-Harthi said on Sunday the Court of First Instance in Muscat had found Said Jadad, who took part in 2011 opposition protests, guilty of "undermining the prestige of the state", inciting the public to join an illegal gathering and using the Internet to publish materials that disturb public order.

Along with his jail sentence, Jadad was also ordered to pay fines totalling $4,470, the reuters news agency reported.

The lawyer said Jadad intended to appeal against the ruling.

Oman has tried to clamp down on public dissent, arresting rights activists who criticise authorities on social media.

Omani online newspaper Mowatin said the charge of undermining the state stemmed from a 2013 open letter to Obama in which Jadad had expressed "dismay" over US policies regarding human rights in the Gulf region.

"We expect the United States, being a superpower, to always stand by the people and to support the principles of democracy and human rights," Jadad wrote.

The newspaper said Jadad's lawyer had argued in court that the message came under the right to freedom of opinion and expression and that the accused had personally suffered from human rights abuses, including being detained for seven days without a warrant and having his documents seized without a court ruling.

Source: Reuters