An autopsy and preliminary tests on Slobodan Milosevic's blood found no evidence of poison or medicines in concentrations that could have killed him, the U.N. war crimes tribunal said Friday.

People walk past a photo of the late former Serbian and Yugoslav president Slobodan Milosevic in the Socialist Party of Serbia local headquarters in Pozarevac, southeast of Belgrade, Serbia and Montenegro, Thursday, March 16, 2006. Milosevic will be buried on the grounds of his estate in Pozarevac on Saturday. [AP]

Tribunal President Judge Fausto Pocar also said an outside investigation will be conducted on the running of the U.N. detention center where Milosevic was held during his four-year trial and where he died last Saturday.

The former Serb leader was ruled to have died of a heart attack, but questions were raised about the cause of the fatal cardiac problem after it was reported he had been taking medicines that were not prescribed by the U.N. cardiologist.

"No evidence of poisoning has been found," Pocar said, reading the preliminary results of a Dutch toxicological report.

A number of prescribed medications were found in his body, "but not in toxic concentrations," he said.

He also said no traces were found of the powerful antibiotic rifampicine, which a Dutch toxicologist had reported finding in a blood sample taken from Milosevic earlier this year.

Rifampicine, which affects the liver's ability to break down enzymes, was thought to have blunted the effect of the beta-blockers he was taking for his blood pressure, leading to speculation that it could have contributed to his death.

The drug disappears quickly from the body. The report said it was unlikely it "had been ingested or administered in the last few days before death."

Further tests were being conducted by the Netherlands Forensic Institute, which conducted the autopsy on Sunday, Pocar said, and the conclusions were only provisional.

Confidential tribunal records from the trial were released to the pathologists to help in their investigation, he told reporters at the tribunal.

The results of the tests were delivered by the Dutch prosecutor's office to both the tribunal registrar, Hans Holthuis, and to Milosevic's lawyer, Zdenko Tomanovic, Pocar said.

Tomanovic and Milosevic's son Marko, who came to The Hague to claim the body and send it to Belgrade for burial, have said Milosevic was killed, and accused the tribunal of responsibility for his death.

Many of Milosevic's supporters in Serbia believe he was poisoned.

Holthuis, the tribunal's administrative head, ordered an external investigation to find out how Milosevic obtained drugs he was not supposed to have.

Tribunal officials earlier said he also had regular access to alcohol.