The ex-Bosnian Serb army chief Ratko Mladic refused to testify in the case against Radovan Karadzic at the International Criminal Tribunal for the former Yugoslavia (ICTY).

The former Bosnian Serb leader Karadzic, who is facing 11 charges for crimes against humanity, called in his former ally to testify in his defense.

Denouncing the UN tribunal as "satanic", Mladic refused to testify, as this could prejudice his own case, the BBC reports.

"This is a satanic court, which is putting on trial us Serbs because we are defending our people from you", Mladic said.

Karadzic read out all of his 6 questions, which he had prepared for Mladic, but the reply was the same in each case: "I refuse to testify on the grounds of my health and because it may prejudice my rights as an accused".

Lawyers representing Mr Mladic say he suffers from a memory disorder that makes it hard for him to differentiate between truth and fiction.

Karadzic was hoping that his former ally's testimony would support his claims that the orders to commit war crimes had not come from him.

In the 1995 Srebrenica massacre, Bosnian Serb forces overran the UN-defended safe area, subsequently killing more than 7,500 Muslims, in what was Europe's worst atrocity since World War II.

Ratko Mladic, who was the general in charge of the troops at the time, is also being tried at the ICTY. He was arrested in 2011 in northern Serbia, after 16 years on the run.