The bombers have launched many challenges against their sentences
The US and Australian embassies in Indonesia have received bomb threats, as three Bali bombers await execution.
A US embassy spokesman said the threats were being taken seriously and staff were working closely with police.
Police spokesman Abubakar Nataprawira said the threat was sent via a telephone text message to police, as was a hoax threat received on Monday.
Three men convicted for the bombings in Bali in 2002 that killed 202 people are expected to be executed within days.
The men - Imam Samudra, Amrozi Nurhasyim and Ali Ghufron (Mukhlas) - were sentenced to death five years ago.
Police in Jakarta said they are investigating the source of the latest bomb threats.
On Monday, a threat against a shopping mall in Jakarta had proved to be a hoax.
Security at the US and Australian embassies has been boosted.
In Cilacap, the coastal town facing the Nusakambangan prison island off the south coast of Java, the port has been closed and barbed wire erected to keep crowds at bay.
Australians have been warned to think carefully before travelling to Indonesia. They made up the largest number of victims of the Bali attacks.
Concerns have risen about the possibility of revenge attacks from supporters of the bombers, whenever they are executed.
A last-minute appeal by relatives of the bombers has been rejected in comments by a Supreme Court judge.
The judge, Djoko Sarwoko, said the latest appeal would have no impact on the timing of the execution.
"A judicial review will not delay the implementation of the verdict, even for the death penalty," said Mr Sarwoko, who is a spokesman for the court.
The Supreme Court has previously thrown out requests for a judicial review, while the Constitutional Court also overruled a petition from the bombers arguing the country's method of execution by firing squad was inhumane.
Despite their frequent appeals for leniency the three have also said they are keen to be "martyrs" for their dream of creating a Southeast Asian caliphate.
Family members now gathered in Cilacap have been refused permission to visit the three men.
Officials have previously said the three men would be shot dead in early November. No date has been announced.