Judges said doctors for the 62-year-old former Yugoslav president had warned that he urgently needed rest, and said they would review plans on how to continue.
``The trial chamber is clearly of the view that the time has come for a radical review of the trial process and the continuation of the trial is needed in light of the health problems of the accused,'' presiding Judge Patrick Robinson said.
Prosecutors appealed to the court to impose a defense lawyer on Milosevic, who has insisted on representing himself since the trial began in February 2002. Milosevic angrily rejected the proposal.
``It is out of the question as you know, nor will I ever agree to it,'' he said.
Milosevic appeared relaxed, vigorous and fit in the courtroom, and objected when Robinson began discussing his medical file but was overruled.
He nevertheless accused the judges of ordering him to appear, despite a doctor's report earlier Monday that he should remain at the nearby U.N. detention center to rest.
He asked for a further month's delay to make up for time he lost preparing his case due to his health problems. The judges said they would rule later on his request and on the prosecutor's proposal for appointing defense counsel. A tribunal spokesman said the decisions would likely be announced Tuesday.
Reading from a physician's report from Friday, Robinson said Milosevic had suffered ``organ damage'' to his left ventricle due to high blood pressure and that it would not be sensible for him to begin presenting his defense as originally planned.
Steven Kay, one of the independent lawyers assigned to ensure a fair trial for Milosevic, said fresh medical evidence and the steady deterioration of Milosevic's health put the continuation of the case in question.
The judges must consider ``his very fitness to stand trial at all,'' Kay said, but in any case, ``he is plainly not fit enough this week'' to appear in court.
Milosevic had been scheduled to give a four-hour opening statement. during which he had been expected to deny responsibility for atrocities committed during the wars in Croatia, Bosnia and the Serbian province of Kosovo, and accuse Western governments of hypocrisy.
``What is happening here is not in the realm of law at all, but in the realm of politics and the media,'' Milosevic said, denouncing the judges for destroying his health.
The trial had been due to resume after a four-month break since the prosecution wrapped up its case. Prosecutors questioned nearly 300 witnesses and introduced reams of documents, videos and other evidence.
Milosevic's courtroom tactics may foreshadow what to expect from former Iraqi President Saddam Hussein, the second former national leader to be accused of war crimes. Milosevic has so far used his trial as an opportunity to grandstand for supporters.
He has pleaded innocent to any wrongdoing, and has challenged the authority of the court. His strategy will likely include an attempt to blame the U.N. member states that created the court, especially the United States and its NATO allies, for alleged war crimes of their own.
Milosevic has argued in the past that a 1999 crackdown he ordered on ethnic Albanian Muslims in Kosovo was undertaken to protect the Serb minority there. He claims NATO's 78-day bombing campaign caused civilian deaths.
He also claims that as president of a crumbling Yugoslavia in the early 1990s, he did not have control over ethnic Serb troops in neighboring Croatia and Bosnia. An estimated 200,000 people on all sides died in fighting that came with the disintegration of Yugoslavia.