Kuta – Indonesia vowed yesterday to hunt down five Bali bombers who are still at large one year after the attack as more than 2,000 mourners held an emotional service to commemorate those killed.

"Make no mistake that those outstanding suspects will be hunted down," top security minister Susilo Bambang Yudhoyono told the crowd. "History will condemn them for ever."

The Al-Qaeda-linked Jemaah Islamiah (JI) regional terror group, which is based in Indonesia, staged the attack on two crowded nightclubs, killing 202 people from 22 countries. Indonesian police, with crucial help from Australian investigators, have caught 34 people and put most of them on trial. Three have been sentenced to death by firing squad and others have been given long jail terms.

But Bali police chief I Made Mangku Pastika, who led the hunt, warned on Saturday that the five have built two more bombs and could be planning further attacks.

A Malaysian who built the Bali bombs, Dr Azahari Husin, and his Indonesian assistant Dulmatin are among those being hunted. Police say Dr Azahari, a former university professor, was involved in a Jakarta hotel bombing in August which killed 12 people.

Inspector-General Pastika said the new bombs are hard to detect by conventional metal detectors but he did not think the devices are in Bali.

"There are some suspects of the Bali bombing still out there and they have also become smarter. So it is the reality that we need to develop new tactics and strategy to catch them," he said.

"We have to realise that these bombs don't contain metal. All of them are plastic so our metal detectors are not very useful for us." He said the suspects have stopped using e-mail and telephones.

"Now they are using ... more conventional, traditional communication – sending people. As long as they don't use electronic communication it is harder for us to catch them." But he said police doubled their intelligence squad and equipped it with more modern surveillance equipment.

"As we understand it, the JI cells in Indonesia are still in the community ... but this is not a formal organisation, so we don't have a list of members, the ID cards. So what I believe now is they are hiding themselves, keeping a calm, low profile," he said.

Apart from the Bali and hotel blasts, JI is also blamed for bombing attacks on churches and priests in Indonesia on Christmas Eve 2000 which killed 19 people and for a string of other attacks.