MOSCOW (Reuters) - A Moscow court jailed a Russian journalist on Thursday after finding him guilty of organizing an extremist group and attempting to overthrow the authorities in a trial denounced by human rights groups as politically motivated.

Investigative reporter Alexander Sokolov, 29, was arrested in July 2015 when he worked for the RBC media group, which has since been sold to the owner of a pro-Kremlin tabloid. Sokolov was sentenced to three-and-a-half years in jail on Thursday. He had denied the charges.

Prosecutors said Sokolov had created an “extremist organization” called “For Responsible Government” - a reference to an Internet campaign which he and three others had conducted to make politicians more accountable.

Reporters Without Borders, a Paris-based press rights organization, had denounced the charges against Sokolov as “spurious” while the Russian human rights group Memorial said Sokolov and his co-defendants were “political prisoners”.

Taking into account the time he has already spent in custody, Sokolov will have to serve only a year and a half in jail. Two of the his co-defendants were sentenced to four years and the third was given a suspended sentence.

As an investigative journalist Sokolov had been researching, before his arrest, alleged embezzlement of 93 billion roubles ($1.55 billion) of public funds during the construction of a new cosmodrome in the Far East, a brainchild of President Vladimir Putin.

Fellow journalists had asked Putin at news conferences to intervene in Sokolov’s case and on one occasion the Kremlin leader had said he would look into his case.

After sentence was pronounced, Sokolov defiantly spoke out in defense of his and his co-defendants’ action in calling on the Internet for a referendum into the conduct of the authorities.

“The idea of holding a referendum against the present-day authorities was recognized to be an extremist one. But we have not finished yet, we will keep fighting,” Sokolov said from a metal cage in which he was kept during the trial.

A tee-shirt he was wearing was emblazoned with the words: “Banning a referendum is extremism.”

($1 = 59.8185 roubles)

(Removes erroneous reference to RBC group being under government control)