CILACAP, Indonesia (AFP) - A jailed Indonesian firebrand cleric on Tuesday (Jan 12) challenged his conviction for funding a militant group in court, as a hundreds-strong crowd chanting "God is great" rallied in support of the Islamist preacher.

Abu Bakar Bashir is regarded as the spiritual leader of militant Islam in Indonesia, and was thought to be a key figure in regional terror network Jemaah Islamiyah, blamed for the 2002 Bali bombings that killed more than 200 people.

He was sentenced to 15 years in jail in 2011 for helping fund a paramilitary group in Aceh, a staunchly Islamic province in the world's most populous Muslim-majority country, which planned to kill the then president as well as Westerners.

The 77-year-old made a rare public appearance on Tuesday to apply for a judicial review of his conviction in the hope of being freed, travelling to the court in the town of Cilacap, the gateway to the prison island off Java where he is held.

His legal team are arguing that funds Bashir collected were intended to help people in the Palestinian territories, but ended up getting sent to the Aceh group without his knowledge.

However Bashir, a frail, bespectacled man with a bushy white beard, appeared to undermine his own case by admitting to knowing about the group's Aceh training camp during a fiery tirade in court Tuesday.

"The physical and weapons' training in Aceh were aimed at defending Islam and Muslims in Indonesia and overseas, and were an obligation Muslims must fulfil because it is God's order," said Bashir, who was wearing a white turban and white robe.

Bashir also told the packed courtroom that the judges should repent for acting against the Quran.

Tuesday's hearing was brief. Prosecutors will respond to the lawyers' arguments later this month.

About 500 supporters, most of whom were dressed in white Islamic skullcaps, packed out the courtroom and gathered outside, and more than 1,000 security personnel had been deployed.

"Bashir is a cleric, not a terrorist," a supporter shouted, while others yelled "God is great, God is great" and thrust their fists into the air.

Bashir, also co-founder of an infamous Islamic boarding school known for producing militants, was previously jailed over the Bali bombings but his conviction was quashed on appeal.

Indonesia was hit by several Islamic militant attacks between 2000 and 2009 but a crackdown weakened the most dangerous networks.

The authorities last month foiled terror plots by several radical Muslim groups, some linked to the Islamic State group, including plans for suicide bombings.