President Milosevic said on Monday he would accept the general principles of a settlement plan by the G8 group of nations conditions for ending the Kosovo conflict.

But Mr Robertson told the Ministry of Defence daily briefing on Tuesday that President Milosevic's indication may be an attempt to "ferment disunity" within Nato.

Mr Robertson said: "He has broken promise after promise. His track record leads to one conclusion: We must not and cannot trust his words.

President Milosevic has "broken promise after promise", George Robertson says

"We will judge him on what he does. We are a long way away from being satisfied with the words that he uses."

Although Serbia had previously issued similar statements, it was the first time acceptance of the G8 terms had come from the top of the regime, sparking hopes of a diplomatic breakthrough.

The crucial factor will be what sort of international military presence President Milosevic is ready to accept in Kosovo.

Mr Robertson said President Milosevic had to accept an international peacekeeping force with a heavily armed Nato component at its core.

Otherwise Nato would be unable to guarantee the safe return of the refugees, he said.

Earlier, Mr Robertson told the BBC the fact that President Milosevic faced a huge economic crisis had led to him to consider backing down.

George Robertson: There would be no diplomatic solution were it not for the air attacks

The defence secretary said: "With the economy in crisis, there is now growing dissent within Serbia which is leading him to look more favourably on the conditions set by the international community - but there is still some distance to go.

"If he is now accepting there should an international force inside Kosovo then that is indeed progress, but it's not really Nato that has to be satisfied here.

The refugees must feel safe to return home, the UK says

"They have to satisfy the people who have been evicted from Kosovo. They are ones who will only go back to Kosovo - and that is what this is all about - if they are satisfied they can do that, and they'll only be able to do that if there is Nato command and control at the very core of that security force."

Nato could accept working in partnership with countries such as Russia in policing a peace in Kosovo, but the force would have to retain allied command structures, the defence secretary stressed.

Challenged on the continuing civilian victims of the Nato bombing, Mr Robertson said some errors could not be avoided in war, but relatively few mistakes had occurred.

The day after it hit a sanatorium, killing 17 people, at least another 10 died in a missile attack on an apartment block in Novi Pazar, in the south west of Serbia.