A UN tribunal in The Hague has acquitted two former Serbian security officials who were accused of war crimes and crimes against humanity committed during the 1990s Bosnian War.

Judges said on Thursday that there was insufficient evidence to show that either man had assisted soldiers who allegedly were responsible for murder and other crimes.

The verdict at the International Criminal Tribunal for the former Yugoslavia for Franko Simatovic, known as "Frenki", and Jovica Stanisic, or "Ledeni" - Serbian for "ice-man" - follows a three-year trial.

Al Jazeera's Katarina Drlja, reporting from The Hague, said: "As soon as the judge acquitted both of them, we could hear gasps of disbelief, of shock, from the representatives of the war victims.

"They couldn't find the words to describe how they feel."

They had expected a guilty verdict, she said.

Stanisic was the head of Serbia's secret police, and widely regarded as the second-in-command of the former Serbian leader Slobodan Milosevic.

Simatovic was the head of special operations in the secret police.

Both were accused of setting up paramilitary forces dedicated to ridding Croatia, and Bosnia and Herzogovina, of all non-Serbs.

Serbia hailed the decision, with Prime Minister Ivica Dacic saying the country "has always advocated fair trials to all those accused before the tribunal in The Hague as the only way to establish the truth about the war and make conditions for reconciliation, peace and stability in the region."

The pair are now free to leave as soon as procedures are completed.

Drlja said that prosecutors were allowed to file an appeal. "This first step has to happen within 30 days," she said.