The report came hours after Milosevic's legal adviser revealed a letter the late Serb leader wrote on Friday, one day before his body was discovered in prison, alleging that he was being poisoned.

In the report by state broadcaster NOS, a lawyer and commentator for the channel, Heikelina Verrijn Stuart, said she had confirmation that doctors first noticed the medicine in his blood in January.

Stuart said the drugs interfered with other medicine Milosevic was taking for high blood pressure and vascular disease.

"They were counterproductive," said Stuart, a lawyer who has closely followed the proceedings. "What we do know is that this is the cause of death and you can't say that it was really a case of natural death."

Stuart said the tribunal only learned of the presence of the drug in his blood last week, on March 7.

"It's naturally a riddle," she said.

Dutch doctors conducted a post mortem examination on Milosevic's remains on Sunday, but the results were not expected to be released until Monday.

A tribunal spokeswoman said she could not comment on the news report. "We don't have any information. We simply have to wait for the results" of the autopsy report, said Alexandra Milenov.

Doctors found traces of the drug when they were searching for an answer to why Milosevic's medication for high blood pressure was not working, the report said.