INDONESIA has moved the three ringleaders of the 2002 Bali bombings on death-row because of security concerns at their prison in Denpasar.

The men were transferred in three armoured cars and guarded by about 30 heavily armed police.

Their move to a higher security jail came on the eve of the third anniversary of the October 12, 2002 bombings in which 202 people died, including 88 Australians.

So-called smiling assassin Amrozi bin Nurhasyin, Imam Samudra and Mukhlas – all awaiting execution – were moved this afternoon from Bali's Kerobokan Prison to Batu Prison on Nusakambangan, an island off the south Java coast, Bali justice ministry spokesman IG Rata said.

The high-security jail is home to former Indonesian dictator Suharto's son, Tommy, who is serving a 15-year sentence for masterminding the murder of a supreme court judge.

"They were moved for security reasons," Mr Rata said. He said the transfer order had come directly from Indonesian Justice Minister Hamid Awaluddin in Jakarta.

He said the letter arrived yesterday but the transfer had been planned for more than two months.

"The soil at Kerobokan and the walls are too fragile and the prison is too full," he said.

"There is only capacity for 338 prisoners there but there are now more than 800 in there."

Batu Prison, about 250km south-east of Jakarta, is known as Indonesia's Alcatraz".

The jail is home to the country's most dangerous criminals.

The overcrowded Kerobokan Prison is where Australian convicted drug smuggler Schapelle Corby is serving her 20-year jail term. It also houses the so-called Bali Nine, whose trials for alleged drug trafficking began today in Denpasar.

Indonesian police have questioned the three death-row bombers over the recent triple suicide blasts in Kuta and Jimbaran, which killed 20 people including four Australians.

Yesterday more than 100 Balinese had staged an angry protest demanding the immediate execution of Amrozi and two other attack ringleaders who are on death row.

Protesters were expected to rally outside Kerobokan prison tomorrow to demand the immediate execution of the trio.

AFP Photo: Bali's anti-terror policemen guard one of five Bali bombing convicts as he is transferred from...

The angry demonstrators at Denpasar's Kerobokan jail managed to remove the prison's main steel door from its hinges but police stopped them getting inside, an AFP correspondent reported on Wednesday.

"Kill Amrozi, kill Amrozi!" the crowd yelled, referring to one of three people sentenced to death by firing squad for the 2002 nightclub bombings which killed 202 people.

Amrozi and the other two on death row, Imam Samudra and Mukhlas, had been transferred the previous day to a high-security island prison off neighbouring Java island following earlier angry protests.

The confrontation was temporarily defused by the arrival of a group of traditional musicians from a nearby village, who positioned themselves between police and protesters.

But the shouting, drum-beating crowd had not yet dispersed.

One demonstrator tied a banner on the prison wall reading: "Hello SBY (Indonesia's president Susilo Bambang Yudyoyono). Kill the person who has hurt Bali (Amrozi)."

Three rows of police armed with batons and shields stood outside the prison's main entrance but did not immediately try to disperse the crowd.

Passions were running high on Wednesday, the third anniversary of the 2002 blasts, and in the wake of October 1 bombings which killed 20 people plus three suicide attackers on the island.

"Kill Amrozi now!" yelled some protesters.

"We are angry he has been moved from here," said Endra, 30.

"We feel Amrozi is being protected by the government. Balinese are very angry."

Amrozi was dubbed the "smiling bomber" for his courtroom demeanour which particularly enraged the residents of Bali, a Hindu enclave in mainly Muslim Indonesia.

Some members of the crowd said they had received an anonymous mobile phone message about four days ago, calling on people to come to the jail to demand the execution of the Bali bombers.

"I knew of the protest from my friends but what is important is that I came here of my own free will," said Arya, a motorcycle taxi driver.

"What does the head of the jail want? Without any explanation, he secretly moved Amrozi away."