A group of supporters gathered in Mongolia's capital after Ts. Bat was sentenced to three months in prison Tuesday. Image via @ideruugan on Twitter.

A Mongolian man was sentenced to three months in prison on Tuesday for defaming a high-profile politician on social media.

Ts. Bat (@batengineer), an engineer and blogger, was found guilty on Tuesday of defaming the Minister for Roads and Transport A. Gansukh via a series of tweets posted last October in relation to the aviation sector.

The case is the first to see a social media user convicted under the country’s controversial criminal defamation and libel laws.

In response to the verdict, local press freedom groups have re-issued concerns over a perceived recent increase “in threats, harassment and pressure from authorities” to those expressing their views online.

Khashkhuu Naranjargal, executive director of local press freedom group Globe International briefly described the ruling as “a brutal action… (one) completely against freedom of expression and democratic values.”

The case sparked outrage on Twitter, with “#FreeBat” quickly gaining traction online. A small group of tweeters protested in the main square of the capital following the verdict.

The man’s sister, Minister of Culture Ts. Oyungerel, has since described her brother as a “whistleblower” whose imprisonment is “political” in nature.

“My brother is a professional engineer who had a 20-year long career in Mongolian aviation. That’s why he knows what’s happening in Mongolian aviation and if he doesn’t like something, he will express it,” the Minister explained.

Via Twitter, Ts. Bat posted just prior to Tuesday’s verdict that “the truth always wins.”

Minister Gansukh’s office has yet to respond to requests for comment on the ruling.

“(This case) sets a very bad precedent against those who express discontent,” his sister later explained. “Mongolia is a freedom-fighting country… This is very bad news for Mongolian citizens, for Mongolia’s future, and for Mongolian democracy.”

Ts. Bat is expected to launch an appeal against the verdict in coming days.