By Sofia Menchu

GUATEMALA CITY (Reuters) -A Guatemalan court on Wednesday sentenced Jose Zamora, a well-known journalist whose work has criticized successive governments, to six years in prison for money laundering in a case rights groups have branded an attack on free speech.

Zamora was also issued a 300,000 quetzal ($38,339) fine, the court said. He was absolved of charges of blackmail and influence peddling.

Zamora said he would appeal and possibly take the case to the Inter-American Court of Human Rights.

"I feel happy because in the end (the sentence) was arbitrary," he told journalists, smiling and appearing calm after the hearing. "I am still innocent and he is still a thief," he said of Guatamala President Alejandro Giammattei. "Nobody in history is going to take that away from him."

Zamora, 66, has said the case against him is a "political persecution" by Giammattei due to reporting on alleged corruption involving the president and his close allies in Zamora's newspaper, elPeriodico, which shut down in May.

Zamora founded elPeriodico, one of the country's leading investigative media outlets, in 1996.

He was arrested in July last year during a crackdown on prosecutors, judges, human rights activists, journalists and opposition officials, spearheaded by the country's Special Prosecutor's Office Against Impunity (FECI).

FECI assistant prosecutor Samari Gomez, who was arrested last year in relation to Zamora for her alleged role in disclosing confidential information, was acquitted on Wednesday and is set to be released later in the day.

According to the attorney general's office, Zamora allegedly received $38,461 to finance his media outlet, which was not regularly deposited into the banking system.

The case developed rapidly and involved 11 hearings in which the defendant's evidence was not admitted, and eight changes of defense attorneys, some of whom now face their own legal proceedings for involvement in Zamora's defense.

Carlos Martinez de la Serna, program director at the U.S.-based Committee to Protect Journalists, said the conviction showed the government's "desperate attempts" to criminalize journalists and called for Zamora to be released.

"His only 'crime' has been the fearless exercise of his profession," he said in a statement.

The Human Rights Watch's Americas director Juanita Goebertus said that prosecutor's calls or a 40-year sentence showed the "viciousness" of Guatemala's persecution of journalism, adding that the rights group was "very concerned" by investigations into elPeriodico journalists who covered Zamora's case.

($1 = 7.8250 quetzals)

(Reporting by Sofia Menchu; Writing by Sarah Morland; Editing by Brendan O'Boyle and Bill Berkrot)