"Journalists make a fundamental contribution to society by providing information which nurtures enlightened public debate," said UNESCO chief Audrey Azoulay.
"The assassination of journalists is the ultimate form of censorship. The prosecution of such crimes is essential to deter attacks against the media," she said.
"Governments must also protect journalists," she added.
Sudip Datta Bhowmik, 50, a crime reporter with Bengali daily Syandan Patrika and TV channel Vanguard in Tripura, was shot dead allegedly by a Tripura State Rifles personnel at the headquarters of 2nd battalion in RK Nagar, around 30 km from Agartala, on November 21.
Eyewitnesses reported that the journalist had an argument with Nandu Reang, the accused, following which he pulled out his service revolver and shot at Mr Bhowmick. He died on the spot and the personnel was arrested.
Mr Bhowmik is the second journalist to have been killed in the state in the last two months. In September, a 28-year-old television journalist, Santanu Bhowmik, was killed by a mob while covering a clash in Mandai, 35 km from Agartala.