Bosnian Serb ex-army chief Ratko Mladic was 'like a bully' who several times at meetings with UN officials during Bosnia's 1992-95 war threatened to kill civilians, a witness said.
David Harland, who was a civil affairs officer and political advisor to the UN protection force in the Balkans at the time, said Mladic warned of "more military action" when he felt Bosnian Serb politicians had failed to achieve results in negotiations.
"We would be in a meeting with him and he would say those around him, his military colleagues... felt that the political civilian leadership did not do well and they might undertake further military actions," Harland told the Yugoslav war crimes tribunal in The Hague.
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Asked by prosecutor Dermot Groome whether Harland perceived "threats to kill civilians in Bosnia's eastern enclaves" as idle, Harland said: "He (Mladic) actually made the threat several times."
"He was like a bully. If the opportunity arose he would do it," he said.
The second witness to testify for the prosecution, Harland on Tuesday also told how 1,000 shells per day on average hit the besieged Bosnian capital Sarajevo throughout most of the war.
"On average we counted about 1,000 heavy weapons impacts... in Sarajevo. This happened while I was there, which was most of the war," Harland said.
He added: "We frequently pointed out to the (Bosnian) Serb leaders that the shelling of the city served only to terrorise the population and cause casualties and did not improve their political situation."
Groome asked whether Mladic was present when UN personel made these statements with Harland answering: "Yes".
Mladic, 70, has been indicted by the International Criminal Tribunal for the former Yugoslavia on 11 counts of genocide, war crimes and crimes against humanity for his role in Bosnia's war.
The man dubbed the "Butcher of Bosnia" faces charges relating to the massacre in the enclave of Srebrenica in northeastern Bosnia in 1995, when almost 8,000 Muslim men and boys were murdered by Bosnian Serb troops under Mladic's command.
It was the worst massacre on European soil since World War II.
He also faces charges for the terrorising Sarajevo during 44 months of shelling and sniping which killed 10,000 people.
Prosecutors also accuse him of taking UN peacekeepers hostage and having ordered his troops to drive out Croats, Muslims and other non-Serb residents from Bosnian towns.
Mladic was arrested in northeastern Serbia last year after some 16 years on the run and subsequently was moved to The Hague. He has pleaded not guilty to the charges. If convicted, he could face life in prison.
Harland's testimony is expected to be followed by five others, including one of the 450 Dutch UN peacekeepers who were guarding the "protected" enclave at Srebrenica when it was overrun by Mladic's forces in mid-July 1995.
Former Bosnian Serb political leader Radovan Karadzic is also on trial before the ICTY, with both men accused of being the masterminds of a criminal plan to rid multi-ethnic Bosnia of Croats and Muslims.
Mladic's one-time mentor, former Serbian president Slobodan Milosevic died in The Hague four years into his own genocide trial in 2006.
