Pham Minh Hoang, who holds dual nationality, "should not be in prison", the media rights group said in a statement released late Wednesday following the conviction.
The 56-year-old, the latest peaceful democracy advocate to be convicted in Vietnam, was accused by a Ho Chi Minh City court judge of "blackening the image of the country" in a series of articles under the pen name Phan Kien Quoc.
France has called for the verdict to be reconsidered.
Paris-based Reporters Without Borders (RSF) said Vietnam`s Prime Minister Nguyen Tan Dung, recently handed a second term, "has instigated a crackdown that bodes ill for journalists, bloggers and free speech defenders".
"(Hoang) is a citizen who just expressed his views on matters of interest to Vietnam. His conviction reflects a dangerous trend in Vietnam towards `Chinese-style` censorship," the watchdog said.
Hoang has already spent one year in custody, which will count towards his jail sentence. This will be followed by a further three years of house arrest.
RSF said security officers, who were armed with clubs, "tried to intimidate journalists" during the half-day trial. Vietnam is ranked 165th out of 178 countries in RSF`s press freedom index.
Dozens of peaceful political critics have been sentenced to long prison terms since Vietnam launched a crackdown on free expression in late 2009, according to Amnesty International.
(Uu.H-AK)
Editor: Priyambodo RH
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