The suspects stand accused of being linked to, or having prior knowledge of, the deadly blast, the second high profile terrorist bombing aimed at foreign interests in the world’s most populous Muslim nation.
“I can't yet provide information on anything significant related to the Marriott bombing,” National Police Chief General Da'i Bachtiar told Reuters. “Law enforcement steps continue but this not yet the time to publicise something significant.”
The Media Indonesia daily quoted a source at Jakarta police headquarters as saying the nine included one Malaysian.
Though no group has yet claimed responsibility for the attack, most analysts believe it to be the work of Jemaah Islamiah (JI), blamed for last year's Bali bombing which killed 202 holiday makers.
Eleven Indonesians and a Dutch banker died when the car bomb exploded outside the American-run Marriott hotel on 5 August. Among the dead was Asmar Latinsani, who police suspected to have detonated the bomb.
Unidentified sources told Reuters that a suicide squad, known as Laskar Khos or Special Force, was active in Jakarta and was believed to have played a role in the blast.
Separately, the Australian government warned that armed groups may be planning an attack to coincide with Indonesia’s national day on 17 August.
“I last week made it clear that we were concerned there could be attacks during the period 10th to the 17th of August, we've gone past the 10th, the 17th is Indonesia's national day so it's a day where this sort of thing could happen,” Foreign Minister Alexander Downer told reporters.
Downer urged Australians to avoid all unnecessary travel to the archipelago.
“What's clear is we have already anticipated that but we aren't talking about a specific date or place,” General Da'i Bachtiar told Reuters, in response to the specific warning from Australian Foreign Minister Alexander Downer.
“We are continuing to anticipate where and when an attack will be carried out, to guard against it,” Bachtiar added.
Indonesian investigators note similarities between the Marriott blast, last October's Bali bombings, and an explosion outside the home of the Philippines ambassador in 2000.
A suicide bomber was involved in the Bali blast. Police have linked that attack to JI, accused of ties to al-Qaeda.
“Whoever did it are Muslim people who have no idea about the real conditions of their own people and they have no humanity at all,” said Neris, 23, a taxi driver whose uncle, Syamsuddin, was killed outside the Marriott.
“It is the Muslim people who are now suffering because of the bombing,” she said.
On Thursday morning, an Indonesian judge said Imam Samudra, charged with masterminding the Bali bombings, would be sentenced on 10 September.
Samudra, a 33-year-old computer expert, responded to the prosecution’s demand he should be sentenced to death by raising his right hand in the air and shouting “Allahu Akbar” (God is greatest).
Previously he has said execution by firing squad will bring him closer to God. His co-conspirator, Amrozi, daubed “the smiling bomber,” was last week handed the death penalty.
Both are members of JI, and studied under the tutorage of elderly cleric Abu Bakar Ba’asyir, also on trial in Jakarta. Ba’asyir is charged with treason linked to his alleged leadership of the group.
"I'd like to say thank you to the prosecution team, which has demanded the death sentence. Because in death we live peacefully, and in death we draw near to God,” Samudra told the court.