Jakarta – A police officer testified yesterday that he had overheard Jafaar Umar Thalib, the leader of the Laskar Jihad militia, urge his followers to wage war on Christians in the religiously divided eastern province of Maluku.

The trial of Jafaar, one of Indonesia's most notorious militants, is being watched closely as a test of Jakarta's willingness to curb religious extremism. The government had touted Jafaar's arrest in May as evidence of the government's cooperation in the US-led war on terrorism.

Prosecutors are basing the charges on a speech Jafaar allegedly gave in April, in which he instructed his followers to ignore a government-sponsored peace agreement between the rival factions in Maluku.

In the speech, he also allegedly insulted President Megawati Sukarnoputri. Two days later, masked gunmen attacked a Christian village in the province, killing 12 people.

"I heard Jaafar say that from today there will be no more talk of reconciliation," said policeman Ferry Ukolli, who had been on guard outside the mosque where the militant leader gave the speech. "Then he said: 'Go home and prepare for war.' I heard the speech clearly. It drew my attention because there was talk of war," he testified.

Prosecutors also played a recording of the alleged speech in which a speaker can be heard urging his followers to "go home and prepare bombs".

The East Jakarta District Court was packed with about 150 of Jafaar's supporters. Dressed in robes and wearing white headdresses, they booed and heckled the witness.

Jafaar – who has denied the charges – appeared relaxed during the hearing. His attorneys argued that Mr Ferry's testimony was unreliable because he is a Christian and was not inside the mosque at the time.

If convicted, Jafaar could face six years in prison. He remains free pending the verdict.

Laskar Jihad is blamed for fomenting the bloodshed in Maluku where as many as 9,000 people died since 1999.