ISTANBUL (Reuters) - A Turkish court handed an additional jail term to prominent journalist Ahmet Altan for terrorism charges on Wednesday, state media said, two weeks after he was sentenced to life in prison in a case that has drawn international censure of Ankara.

Altan, his brother and four other journalists were sentenced this month for aiding plotters of a 2016 failed coup, charges they deny. The Altan brothers were accused of giving coded messages on a television talk show a day before the coup attempt.

The verdict drew criticism from rights groups and international bodies, including the United Nations. It is widely seen as the latest example of a crackdown under President Tayyip Erdogan. Since the coup more than 50,000 people have been jailed and more than 150,000 sacked or suspended from their jobs.

On Wednesday, a court sentenced Altan to a total of five years and 11 months on two different charges related to an article he wrote for the Haberdar news website, the state-run Anadolu news agency said.

The court ruled the language he used to describe the Kurdish conflict in southeast Turkey - where he wrote of “children” digging trenches to fight Turkish soldiers - attempted to portray the actions of the outlawed Kurdistan Workers Party (PKK) as innocent, Anadolu said.

The PKK, considered a terrorist organization by the United States, the European Union and Turkey, has waged a three-decade insurgency in the largely Kurdish southeast.

The court also ruled the same article had insulted Erdogan, Anadolu said. Insulting the president is a crime in Turkey.

Hours after the verdict was announced, Britain’s Guardian newspaper published an open letter signed by 38 Nobel laureates, including Kazuo Ishiguro and J.M. Coetzee, addressed to President Tayyip Erdogan. It described the evidence against the Altan brothers and the four others who were sentenced to life as “insubstantial”.

“All these writers had spent their careers opposing coups and militarism of any sort, and yet were charged with aiding an armed terrorist organization and staging a coup,” it said, calling for their acquittal and Turkey’s return to rule of law.

Altan, a well known journalist and author who had previously been editor of the now-defunct liberal newspaper Taraf, was detained for some 17 months before his life sentence was handed down this month.

“We will spend the rest of our lives alone in a cell that is three meters long and three meters wide. We will be taken out to see sunlight for one hour a day,” he wrote in a New York Times essay published on Wednesday.

“We will never be pardoned and we will die in a prison cell.”

(Corrects paragraph eight to read sentenced to life, not sentenced to death.)