Bali police chief Major-General Made Mangku Pastika on Tuesday said two people had been taken in on Sunday for questioning in connection with Saturday night's bombings at beach restaurants, which a hospital official said killed 22 people and wounded 135.
"We have some progress," he said. "We hope to find clearer clues but not all has been reported to me."
But deputy national police spokesman Soenarko Artanto made clear there had been no formal arrests. "What we have right now are 39 witnesses," he said.
Under Indonesian law police may hold people for questioning for several days without bringing charges or arresting them. There was no word on how many had been released.
The two who were taken in on Sunday have not been officially named as suspects. Pastika said they were not Balinese.
Three bombs tore through restaurants packed with evening diners on Saturday. Two were outdoor seafood restaurants on Jimbaran beach and one a steak bar at Kuta beach.
At the top of the suspects list are Malaysians Azahari bin Husin and Noordin Mohamed Top, fugitive leaders of the Jemaah Islamyiah network.
Police say the group was behind the first Bali bombings in 2002, which killed 202 people, and that Azahari and Top helped plan that and subsequent deadly attacks on a luxury hotel and an embassy in Jakarta.
There were no immediate claims of responsibility for the blasts, which has usually been the case in Indonesian bombings, but Artanto said Azahari and Top were prime targets of the hunt.
"Our original plan from the beginning is chasing these two masterminds. After the recent incidents our hunt for them has been stepped up," he said. He could not confirm there was evidence linking the two men to the latest blasts.
Azahari bin Husin is believed to
be one of the blast masterminds
However, one of the convicted bombers from the 2002 Bali attack said the weekend blasts were also the work of a group led by bomb expert Azahari.
Ali Imron is serving a life sentence for his key role in the earlier bombings but escaped a death sentence because he had cooperated with police in their investigation.
Imron told the Indo Pos newspaper by telephone from Jakarta's Cipinang prison that judging from press reports, he believed the perpetrators were "who else if not the group of Dr Azahari?"
Imron said he came to the conclusion based on details of the methods used, including the deployment of bombers who blew themselves up and the type of devices that were detonated.
"It is said that there was a nine-volt battery found on the sites. If this is true, then my estimate is not wrong. The use of
Combo shot: Suspect (top C)
enters restaurant before blast
nine-volt batteries is a trademark of Azahari," he said.
Imron said he did not recognise any of the three suspected bombers but added: "So far, Azahari has never stopped recruiting new people for his bombings. The three men killed could be his men."
He added: "So far, Azahari always observes. Even more so if the suicide bomber is a new recruit, that would need to be monitored," he said.
Video footage released by investigators this week showed a man in a black T-shirt and jeans strolling into a restaurant, followed almost instantly by an explosion.
The tape and photos of three severed heads believed to be those of the bombers are being widely shown by Indonesian media as the country launches a huge manhunt for those involved.
President Susilo Bambang Yudhoyono on a hospital tour on Tuesday morning with Singapore Prime Minister Lee Hsien Loong - the first foreign leader to visit the island since Saturday's bombings - told one of the victims: "We will chase those perpetrators and bring them to court. Please be patient."
About 200,000 Indonesian police officers are on the highest alert nationwide.
Bashir condemns blast
Indonesian Muslim cleric Abu Bakr Bashir, who is in prison for his role in the 2002 bombings, on Tuesday condemned the weekend blasts.
"I really disapprove of bombings in non-conflict areas for whatever reason, including in Bali, because it can be almost certain that innocent and unknowing victims would fall," Bashir said in a statement released by his lawyer.
Abu Bakr Bashir denounced
the restaurant blasts
Bashir said he was particularly saddened if such attacks claimed the lives of "people whose religion is Islam".
He advised the injured victims and the families of those who died "to accept this fate from Allah" and also advised the Indonesian government to practise God's law better.
"These saddening incidents, in essence, are warnings, scolding from Allah to us all who are not respecting his Sharia [Islamic law]," he said.
Meanwhile, Australia warned its citizens on Monday that the Seminyak district in Bali could be the next target.
The warning was contained in an update to the Department of Foreign Affairs and Trade's website late on Monday that advises Australians to avoid non-essential travel to Indonesia because of the terrorist danger.
"Media have reported further general and specific bomb and terrorist threats and anonymous tip-offs in the wake of the 1 October bombings," the website said.
Australia says Bali's Seminyak
area may be the next target
"While this information cannot be corroborated, Australians should be aware that the Seminyak area in Bali has been mentioned as a potential target for terrorist attacks," it added.
The site also warns that Seminyak nightclubs popular with
Westerners could be at risk.
The government of Indonesia - the world's most populous Muslim nation - has won praise for scores of arrests and convictions since the first Bali bombings, although critics say some key players got off lightly, and note Jemaah Islamyiah has never been declared an illegal organisation.
The opposition Labour Party has called on Prime Minister John Howard to demand that the Indonesian government follow Australia's lead by outlawing the group.