Indonesian police say a man they are questioning has admitted involvement in the bomb attack that killed nearly 200 people at a Bali nightclub last month.

National police chief Da'i Bachtiar said the man, whom he identified only as Amrozi, was the owner of the minivan used in the 12 October attack on the holiday island.

Amrozi (centre) was arrested in East Java

Amrozi's exact role in the bombing remains unclear.

Asked if Amrozi had parked the minivan packed with explosives outside the Sari Club, Mr Bachtiar said: "The group has several people with a division of labour, certainly including Amrozi, who admitted going there and dividing up tasks".

Amrozi was flown to Bali from East Java on Wednesday for questioning. Mr Bachtiar said he had provided "lots of information".

A spokesman for the investigators, Brigadier-General Edward Aritonang, said they were still questioning him.

"There are many things that have to be cross-checked and be studied thoroughly," he said.

The BBC's South-East Asia correspondent Jonathan Head says Amrozi appears to have acted as a field coordinator in the bombing.

Police want more information from Abu Bakar Ba'asyir

But it is still too early to say whether he was a key player or just a minor one, our correspondent says, adding that there have been many false leads in the investigation.

According to a local television report, Amrozi was arrested at an Islamic boarding school in the town of Tenggulun.

The head of the school, Dzakaria, said Amrozi had attended a speech at the school by the 64-year-old radical Islamic cleric Abu Bakar Ba'asyir, who is now being held at a police hospital in Jakarta.

Amrozi "sometimes came to my school to conduct prayer with us," said Mr Dzakaria.

Amrozi is the first suspect to be named over the three blasts which rocked Bali. The minivan bomb was by far the most powerful of the three.

Militant group

Earlier on Thursday the police released a sketch of a fourth suspect wanted in connection with the nightclub bombing.

Police chief Bachtiar: Hunting Amrozi's associates

The main bomb used was packed into a Mitsubishi minivan parked outside the nightclub.

About 120 detectives and intelligence officers from Australia, the US, the UK, Japan and other countries are working on the case alongside Indonesian investigators.

The regional Islamic militant group Jemaah Islamiah, which is allegedly headed by cleric Abu Bakar Ba'asyir, is suspected by some governments of being behind the bombing.

The group is also suspected of having links with Osama Bin Laden's al-Qaeda network.

But the ailing cleric has not been declared a suspect in the investigation.

Mr Dzakaria said Amrozi worked in Malaysia during the 1990s - a time when the cleric was living there in exile during the dictatorship of former Indonesia President Suharto.

It is not clear if the two men ever met in Malaysia.