Asahara, 40, is charged with masterminding the March 20 subway attack, which killed 12 people and made more than 5,000 ill. The trial had been scheduled to begin Thursday in Tokyo District Court.
The development stunned Japan, where the case has been the object of intense public fascination.
Thousands of people had been expected to line up to try to secure seats in the courtroom, and Japanese media had created a tent city of makeshift pressrooms near the court.
There had already been one delay scare earlier this week. The fired lawyer, Shoji Yokoyama, suffered whiplash in a traffic accident Sunday while riding in a car driven by a cult member. Initial reports said that would cause a postponement, but court officials decreed the trial should go on.
With the firing, court officials said the trial could begin as early as Nov. 2 -- when the second session was scheduled -- but acknowledged it was very unlikely a lawyer could be appointed and make the necessary preparations by then.
Analysts quoted by Japanese media said that after this delay, the trial would likely be postponed until the start of the new year.
According to a human rights group trying to help cult defendants find lawyers, Asahara's latest move may be an attempt to buy more time for his defense.
"I don't know if this is Asahara's deliberate strategy, but it certainly will give him more time," said group activist Kenji Chiyomaru.
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