Bombs found in a militant safe house in South Sumatra were packed with bullets to inflict maximum carnage, police said Friday as they interrogated 10 suspected Jemaah Islamiyah (JI) cell members.

Police also said they were on the lookout for fugitive Singaporean terror suspect Mas Selamat bin Kastari after arresting one of his alleged associates, a Singaporean bomb expert identified only as MH, on Saturday.

"They have changed their techniques. The bombs contained not only buckshot but also bullets to give a double impact," national chief police Sutanto said.

"If they had exploded, the bullets would have easily killed people."

Police have given very little information about the men who were rounded up in and around Palembang between Saturday and Wednesday, saying only that they formed a dangerous cell linked to some of the region's most wanted extremists.

Investigators were sifting through volumes of material gathered from the alleged safe house in the South Sumatra provincial capital, including some 20 makeshift bombs and 18 computer hard drives.

They said the cell's senior bomb-maker was the Singaporean believed to be Mohammed Hassan, alias Abu Hamza, who was the subject of a "red note" from the Singapore government warning of his alleged terrorist activities.

He was connected to fugitive Malaysian extremist Noordin Mohammad Top, Indonesia's most wanted man, as well as Mas Selamat, the alleged JI leader in Singapore who escaped from prison there in February and is still at large.

Noordin calls himself leader of Al-Qaeda for the Malay Archipelago and is seen as the head of the most extreme faction of JI, a loose network of Islamist militants in Indonesia, Malaysia, Singapore, the Philippines and southern Thailand.

He allegedly masterminded the 2002 Bali bombings which killed more than 200 people, mostly foreigners, as well as the 2003 Marriott Hotel attack in Jakarta and the Australian embassy attack in 2004.

The Palembang cell had staked out a backpacker cafe in the tourist town of Bukittinggi, West Sumatra, police said, and was reportedly eyeing Western targets in Jakarta.

Police refused to confirm reports that Mas Selamat had entered Indonesia after his dramatic February 27 escape through a toilet window in a detention centre in Singapore.

But they said they would post "Wanted" notices with Mas Selamat's picture throughout the massive archipelago.

Sutanto said police were being circumspect about giving information on Mas Selamat because they were afraid he would escape.

"We don't need to say anything. It's still under investigation. We're afraid that if we mention it he'll escape," he said.

The Singapore government accuses Mas Selamat of plotting to hijack a plane in order to crash it into Singapore's Changi Airport in 2001.

Sutanto said the Singaporean suspect in custody would be prosecuted in Indonesia before Jakarta considered any extradition request from Singapore.

Police have confirmed that Hassan had received military training in Afghanistan but would not comment on local media reports that he had met Al-Qaeda leader Osama bin Laden.

Analysts said the police would be hoping to find a "treasure trove" of intelligence on Noordin and the JI network from the suspects and the computer hard drives.

But Singapore-based expert Dr John Harrison said such arrests only "bought time" for the authorities and sooner or later Indonesia would have to confront the radicals' violent ideology.

The arrests are the most significant blow to JI, which grew out of radical religious schools in Java island in the 1990s, since the capture of senior leaders Abu Dujana and Zarkasi in June last year.

Indonesia has captured or killed around 300 JI suspects in the past six years but several senior leaders such as Noordin remain at large.