Senior Islamic clerics said Wednesday they have been asked to counsel the Islamists on death row for the Bali bombings, in another sign the executions are imminent.

`We have received a letter from the Cilacap prosecutor`s office to send nine clerics to the prison to provide counsel for the trio,` said Sahlan Natsir, a member of the local Islamic clerical body near the prison.

The letter did not specify when the clerics would be asked to visit the bombers -- Imam Samudra, 38, Amrozi, 47, and his brother Mukhlas, 48 -- who have been in isolation awaiting execution since Friday.

Prosecutors have said only that the executions will be carried out by firing squad in `early November.`

The bombings of packed nightspots on the resort island of Bali in 2002 killed 202 people, mostly foreign tourists including 88 Australians, as well as 38 Indonesians.

Security has been tightened across the mainly Muslim archipelago amid fears of revenge attacks from Islamist extremists and the Jemaah Islamiyah regional militant network that allegedly instigated the Bali carnage.

Additional security has been given to President Susilo Bambang Yudhoyono after a threat to his life in the form a letter purportedly penned by the bombers and posted on an Islamist website.

The letter dated August urges Islamist militants to `war against and kill` Yudhoyono and other senior officials in retaliation for the executions.

The United States and Australian embassies were the target of anonymous bomb threats sent to police by text message on Tuesday. Searches of the heavily guarded embassy compounds failed to find any bombs.

Police earlier this week extended a no-go zone around Cilacap port connecting Java to the high-security Nusakambangan prison island off southern Java where the bombers are being held.

Prison chief Bambang Winahyo has said the bombers appear to be calm and ready to die. They are reportedly impatient to become `martyrs` for the Islamic utopia they dream of creating across Southeast Asia.