Widows of Srebrenica massacre victims on Thursday slammed as inadequate the 40 year sentence handed down to former Bosnian Serb leader Radovan Karadzic, as supporters dismissed the ruling as biased.

"He killed so many children and will perhaps live long enough to regain freedom. Where he is is not really a prison. It is warm, he eats, he even looks good," said Bida Smajlovic who lost her husband and brother in the atrocity.

"My pain and my loneliness endure and nothing will change that, nothing can reduce my suffering," she said.

The 63-year-old's husband was one of three brothers who died at Srebrenica.

Almost 8,000 Muslim men and boys were killed and their bodies dumped in mass graves by Bosnian Serb forces in the 1995 massacre, the worst bloodshed on European soil since World War II.

On Thursday, their wives, including Bida, gathered nervously in Srebrenica around a television set to watch war crimes judges in The Hague sentence Karadzic, now 70, who will receive credit for time already spent in detention since 2008.

Another Smajlovic widow, Sajma, wept as she saw Karadzic on television.

"As soon as I see him it angers me," she said, adding that she had taken tranquillisers to cope with the pain of the sentencing.

The International Criminal Tribunal for the former Yugoslavia (ICTY) on Thursday sentenced Karadzic to 40 years in jail after finding him guilty of 10 charges relating to Bosnia's 1992-1995 war, including genocide for the Srebrenica slaughter.

- No sentence 'adequate' -

But Vasva Smajlovic, 73, said no sentence, however long, could compensate her for the loss of her husband Ismet.

"There is no adequate sentence for him, he will perhaps live long enough to be freed and has already lived for a long time, unlike my Ismet," she said.

"The best sentence would be to kill him on the spot, for the world to see him decompose. The fact I have lived to see him condemned brings me some comfort," she added.

In Belgrade after the sentencing, up to 5,000 ultranationalists briefly broke out in chants of "Radovan Karadzic!" during a pre-election rally against the government, which also took aim at the Hague-based tribunal.

"The verdict on Radovan Karadzic is a verdict on all Serb people, all of Serb history and the Serbian nation," Serbian Radical Party leader Vojislav Seselj told the crowds, some of whom let off firecrackers.

"He was sentenced while innocent... just because in a crucial historical moment he led Serbs in Bosnia," said Seselj, who faces his own verdict from the court next week but is excused from attending for medical reasons.

In 1992 Karadzic founded the Republika Srpska (RS), a breakaway Bosnian Serb territory, and the conflict that ensued pitted his forces against the country's Muslims and Croats.

The Dayton peace accord which ended the war in 1995 formalised Bosnia's division into two semi-independent entities -- the RS and a Muslim-Croat Federation.

- Serb stereotypes -

Current RS leader, firebrand Milorad Dodik said it was "absolutely clear that today's verdict... was made under strong pressure from various international lobbies".

He said the ruling was in accordance with "stereotypes about Serbs' exclusive guilt for the war in Bosnia", Beta news agency reported.

Earlier Thursday, Serbian Prime Minister Aleksandar Vucic warned against attacks on the RS in light of the verdict, saying Serbia would "stand with our people, we will protect the right to survive and exist" in the RS.

But in Sarajevo, Bosnian Muslim political leader Bakir Izetbegovic described the conviction as the "most important verdict" since the Nuremberg trials for prominent Nazis.

Other victims of Karadzic's aggression, while drawing some comfort from the ruling, seemed less satisfied.

"I was hoping for a life sentence," said Adil Draganovic, 63, who was held captive in a Bosnian Serb concentration camp during the war and travelled to the Hague for the verdict.

"But then again 40 years is as good as a life sentence for him," he said, while sporting a Bosnian flag around his neck.

In the remote and snowy Montenegrin village of Petnjica, where Karadzic was born, there was further disappointment for different reasons.

Relative Simeon Karadzic, 65, said the war crimes convict had shown a "spirit of tolerance" towards Muslims after moving to Sarajevo in his teens.

"The tribunal... simplified reality too much. All the actors were divided into good and bad."