Indonesian police received a text message threatening that foreign embassies in Jakarta would be attacked if a jailed Muslim cleric was not released.

Security sources were increasingly certain that the suicide bomber belonged to Jemaah Islamiyah, the Islamic militant group that killed more than 200 people in the Bali nightclub bombings two years ago. The group’s alleged leader, Abu Bakar Bashir, is in police custody pending formal charges of involvement in terrorism.

Mr Howard said that further atrocities could not be ruled out. “The information they have available indicates that the number of operatives . . . is sufficiently large to support the fear that there could be another attack,” he said.

Alexander Downer, Australia’s Foreign Minister, who is in Jakarta, said that Indonesian police had received a threat by mobile phone calling for Bashir’s release.

“(They) received an SMS message about 45 minutes before the attack yesterday that there would be an attack on Western embassies unless Abu Bakar Bashir was released,” Mr Downer said. He added that the warning had not been passed to the Australian authorities until after the bomb had exploded, killing nine and wounding more than 180.

Australian investigators in Jakarta said that the bomb, hidden in a green minivan, contained up to 200kg (440lb) of potassium chlorate. The composition was similar to those used by Jemaah Islamiyah in the attacks on Bali and the Marriott hotel in Jakarta; 88 Australians were killed in the Bali bombs.

An Arabic website carried an admission of responsibility from Jemaah Islamiyah, saying that it had “decided to make Australia pay”.

However, terrorism experts have questioned the claim, saying that the website had previously published false admissions of responsibility.

The only Australian citizen seriously injured was Manuela Musu, 5, the daughter of an Australian father and Indonesian mother. She was evacuated to a Singapore hospital yesterday in a serious but stable condition. Her mother was killed in the blast. All those killed were Indonesians, most of them policemen and locals employed to guard the embassy.

Thousands of people flocked to the site, writing messages of condolence and outrage, first on books laid out for the purpose then, when space ran out, on cloth banners and finally on the plywood put up around the site to avoid contamination.

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