DUBAI (Reuters) - A Saudi court sentenced human rights activist Issa al-Nukheifi to six years in prison on Wednesday over tweets critical of the government, a rights group said, confirming a Saudi newspaper report.

Saudi newspaper Okaz said the defendant, who it did not identify, was accused of criticizing Saudi Arabia’s intervention in neighboring Yemen, insulting the government and objecting to its decisions, criminal proceedings and security procedures.

ALQST, a London-based Saudi rights group, identified the defendant as Issa al-Nukheifi, an activist who was detained in December 2016. It condemned the conviction and sentencing.

Amnesty International called for his immediate release.

“Instead of engaging with activists on reforms, the authorities are going after them one by one, with almost all of the country’s human rights activists now silenced or imprisoned,” Dana Ahmed, the group’s campaigner on Saudi Arabia, said.

The Saudi Ministry of Interior declined to comment on Nukheifi’s case.

Okaz reported that his sentence was also for re-tweeting anti-government accounts and simultaneously receiving money transfers from a prisoner still serving a sentence.

Nukheifi was sentenced to six years of prison and, following his release, a six year ban on social media as well as a six year travel ban outside of the country.

Nukheifi was previously arrested, tried and sentenced to prison for similar offences, an Amnesty report said. He was detained in 2012 and released in April 2016, only to be arrested eight months later.

On Tuesday, ALQST published a letter by Nukheifi from custody addressed to Crown Prince Mohammed bin Salman.

“I was very happy listening to your speeches and interviews where you call for freedom of expression and respecting human rights, which is what we call for and work with you to achieve,” he wrote. “I am writing to you from inside my imprisonment, having been detained for asking for these (steps).”

In September, the arrest by Saudi authorities of some 30 clerics, intellectuals and activists was condemned by another group, Human Rights Watch.

Its Middle East director Sarah Leah Whitson said at the time that the arrests were a sign that “Mohammed bin Salman has no real interest in improving his country’s record on free speech and the rule of law”.

Crown Prince Mohammed has rocketed to the pinnacle of power in Saudi Arabia, pushing a reform agenda called Vision 2030 aimed at weaning the country off oil and introducing social reforms. Critics say he is not doing enough to liberalize politics in a country where the king enjoys absolute authority.

In a Washington Post article published on Wednesday, when the crown prince was asked whether he might release human rights activists before his visit to the United States next month, the paper reported him as saying that Saudi standards were different to American ones and “if it works, don’t fix it”.

The paper said he added later through an aide that he would consider reforms in this area, as in others.