US intelligence agencies are convinced that the terrorist group suspected of planning the Bali bombing, Jemaah Islamiah, remains capable of carrying out devastating attacks and is actively planning to target Westerners in South-East Asia.
A senior US Government official has told The Age that JI still has a significant operational arm and up to 500 operatives in the region.
The mounting concerns about JI last night prompted upgraded travel warnings across most of the region. The new alert, issued by the Department of Foreign Affairs and covering Thailand, the Philippines, Malaysia, East Timor, Singapore and Brunei, advises Australians to defer plans for non-essential travel. Existing warnings for Indonesia were reissued on Wednesday.
Local intelligence sources confirmed there were "justified fears based on credible information" of new terror attacks.
The US official spoke to The Age soon before the Riyadh bombings and expressed concern that JI had become a highly mobile network moving its people through South-East Asia.

"We think there are still large numbers of Jemaah Islamiah that are known to us who are planning activities that are connected to al-Qaeda," said the official, who could not be named. "There are transfers of money and there is clearly an intention, and to a certain extent, a capacity to target foreign interests in the region".
The fresh intelligence on JI came as it was revealed that one of the suspects in Monday's suspected al-Qaeda bombing in Saudi Arabia is the older brother of a former key JI operative in South-East Asia.
The Saudi Government has named one of the 19 suspects in the Riyadh attacks as Canadian-Kuwaiti Abdulrahman Mansour Jabarah, whose younger brother distributed funds for terrorist bombings by JI cells.
Jabarah's brother, Mohammed Mansour Jabarah, was arrested in March last year and is now in US custody. An FBI report on his interrogation, given to The Age, revealed that the young Jabarah had attended a meeting of senior JI figures in Thailand just before his arrest where the group decided to attack so-called "soft targets" such as bars and clubs frequented by Westerners in South-East Asia.
JI's operational chief, Hambali, was still on the run but, "still has the capacity to rally troops", said the official who briefed The Age. Hambali was present at the Thailand meeting with the younger Jabarah who was a bag man for JI in South East Asia and allegedly helped finance terrorist plans for attacks in Singapore and the Philippines.
On Wednesday, Foreign Minister Alexander Downer said he remained, "very concerned about Jemaah Islamiah" in the region. Yesterday the US State Department updated its travel warning for Americans travelling to Malaysia because of the "continuing concern about the possibility of terrorist attacks".
The younger Jabarah is believed to have been sent to South-East Asia by al-Qaeda's third in command, Khalid Sheik Mohammed, who is credited with planning the September 11 attacks. Mohammed, arrested in Pakistan several months ago, is in US custody.
The US official who briefed The Age said that the interrogation of Mohammed had provided new evidence of al-Qaeda's links to JI. "We are learning more and more from him every day including (about) Jemaah Islamiah," the official said. "We have always felt reasonably confident that Hambali was the operational link between JI and al-Qaeda and everything we have learnt has confirmed that understanding."
While Hambali's whereabouts are unknown there is new intelligence that Bangladesh is becoming the latest haven for al-Qaeda operatives on the run.
At a closed intelligence seminar in Washington last week, officials suggested that up to 500 JI operatives could still be active in South-East Asia and targeting Westerners at tourist spots in South-East Asia, in particular in southern Thailand and Cambodia. But Singaporean intelligence officials have also expressed fears that shipping lanes and ports in the region could be attacked.
The fresh Department of Foreign Affairs advisories warn travellers to take care in commercial and public areas frequented by foreigners, including shopping centres, clubs, hotels, bars and restaurants. They cover popular holiday areas, like Phuket in Thailand and coastal resorts in the Philippines.