The revelation came during the interrogation of 10 men who were arrested this week on Sumatra Island. Twenty-two explosives also were seized, many packed with bullets to maximise the impact of the blasts, said police spokesman Maj Gen Abubakar Nataprawira.

The busts highlighted the lingering threat in Indonesia, which has been hit by a string of suicide bombings in recent years, including the 2002 Bali nightclubs attacks that thrust the world's most populous Muslim nation onto the front lines in the war on terrorism.

Many of the 240 people killed in the blasts, blamed on the regional militant network Jemaah Islamiyah, have been foreign tourists.

Some of the men rounded up this week said they initially planned to attack Westerners at Kafe Bedudel, a small cafe in the hilly Sumatran resort town of Bukittinggi, even placing timed explosives inside at one point, a senior police officer who took part in the arrests said. He spoke on condition of anonymity because he was not authorised to speak to the media.

They aborted the mission after realising that many of the victims would have been Muslims, deciding instead to choose a target in the capital, Jakarta, said the senior officer, who refused to elaborate.