An Indonesian court jailed an Islamic militant for life for preparing explosives for the Bali nightclub bombings which killed 202 people.

Suranto Abdul Ghoni, who crushed chemicals for the deadlier of the two bombs which ripped through crowded nightspots, is the fourth man to receive a life sentence.

Three others have been sentenced to death for the attack on October 12, 2002, which was staged by the al Qaeda-linked Jemaah Islamiyah terror group to avenge injustice to Muslims worldwide.

"What the defendant has done constitutes an extraordinary crime and crime against humanity," said chief judge Made Sudia.

The bearded Ghoni, wearing a skullcap and a white shirt, was expressionless as the judge read the verdict.

Ghoni, 34, has admitted crushing chemicals for the bomb at the home of convicted bomber Amrozi in Java in September 2002 and taking four boxes of the powdered chemicals to Bali by bus.

He has told the court that until he arrived in the island he did not know what the chemicals were for. Amrozi, one of those sentenced to death, had told him they were for fertiliser.

Ghoni denied charges that he attended meetings to prepare the attack.

But he admitted helping pack explosive materials into a filing cabinet which was placed inside the van that exploded outside the Sari Club. Another suicide bomb went off seconds earlier inside Paddy's Pub.

Ghoni's crimes are punishable by death but judges said he was still young and had behaved politely throughout the trial.

Prosecutors said evidence showed Ghoni attended meetings at Solo in Central Java to prepare the bombings, which killed mostly Australian and other Western holidaymakers.

Courts in the resort island have now sentenced 31 people for the attack. Five others are on trial or under investigation and some key suspects are still being hunted.

The nightclub blasts were the worst terror attack since September 11, 2001, in the United States.