A key military adviser to former Yugoslav President Slobodan Milosevic has told the UN war crimes tribunal there was a direct link between Mr Milosevic and Serb nationalists fighting in Croatia in 1991-95.

The witness, General Aleksandar Vasiljevic, told the Hague tribunal that Serbian units could not have fought in Croatia in the early 1990s without presidential approval.

I do know some Serbian units were at the Slavonia battlefield - it is my opinion that such a decision would have been under the responsibility of the president of the republic General Aleksandar Vasiljevic

During the examination, prosecutors also produced what could be key documentary evidence, in the form of letters from Croatian Serb leaders asking Mr Milosevic to put pressure on the Yugoslav Army to assist them.

General Vasiljevic, who headed army counter-intelligence, said the letters demonstrated that the Croatian Serbs believed the accused had real influence over the army.

Observers describe him as a highest-level insider witness, who has given some of the most important testimony so far.

The general is expected to give evidence for several days, and to be cross-examined next week by Mr Milosevic.

The deposed president has been on trial since last February for war crimes, crimes against humanity and genocide during three Balkan wars, in Bosnia, Croatia and Kosovo.

Prosecution boost

The general said there were several Serbian territorial defence (TO) units operating in Eastern Slavonia, a region in eastern Croatia which saw heavy fighting.

Martic "believed Milosevic controlled the Yugoslav army"

"I do know some Serbian TO units were at the Slavonia battlefield," he said.

"It is my opinion that such a decision would have been under the responsibility of the president of the republic."

Correspondents say the testimony is very helpful to the prosecution, which is attempting to establish Mr Milosevic's responsibility for the actions of Serb paramilitaries.

Control of army

But the letter produced later as evidence attempted to demonstrate that the accused's influence went beyond these forces.

General Vasiljevic said the 1993 letter, signed by the leader of the breakaway republic of Serb Krajina Milan Martic, showed that the Croatian Serbs believed Mr Milosevic controlled the Yugoslav Army as well.

Mr Milosevic was at the time only president of Serbia, and the army was under the command of the Yugoslav president.

And he claims he had no real influence over the army until he became president of the whole Yugoslav Federation in 1997.

"[Martic] is actually addressing the person he believes has factual influence, and could issue orders through the general staff for granting the equipment Martic has requested," General Vasiljevic said.

General Vasiljevic came to the tribunal voluntarily to testify after being named in the indictment against Mr Milosevic, the prosecution has said.

He is said to be a key link in what the court describes as efforts by Serbs to evict Croats from part of Croatia during attempts to create a Greater Serbia.