Jakarta  - Indonesian military authorities stepped up security of President Susilo Bambang Yudhoyono following threats to assassinate him and other senior officials if the three Bali bombers are executed, a military official said Tuesday.

"We will prepare the security as well as possible, from planning to the implementation," Armed Forces Commander General Djoko Santoso was quoted as saying by the state-run Antara news agency.

Police were examining threats on a website contained in a letter purporting to be from the three Bali bombers calling for the death of the president, vice president and other government officials if the executions went ahead.

The threatening letter apparently signed by the three bombers - Imam Samudra, Mukhlas and Amrozi - was written in Indonesian, English and Arabic and was carried on the website www. foznawarabbilkakbah. com.

But police doubted it could have come from the bombers because they are currently isolated in the maximum security prison on Nusakambangan Island, off the southern coast of central Java.

Earlier, police said a telephone text message had been sent anonymously threatening to blow up the US and the Australian embassies in Jakarta if Amrozi and other Bali bombers were executed.

Police search at the embassy compounds failed to find any bombs.

"Nothing is found. The location is safe," the Kompas. com news website quoted police as saying.

Security was boosted across the predominantly Muslim nation, including at the US and the Australian embassies, due to fears about revenge attacks from militants after the execution of the three militants condemned to death for their roles in the 2002 attacks.

In an attempt to save them from imminent execution, lawyers representing the condemned militants on Monday filed another last-minute appeal to Bali's Denpasar district court. But spokesman for the Supreme Court said that a new appeal filed by lawyers for relatives of the militants would not delay the sentence being carried out.

Imam Samudra, Mukhlas, alias Ali Ghufron, and Amrozi, also known as the smiling assassin, face a firing squad for their roles in the bombings of two nightspots on the popular tourist Bali island that killed 202 people, mostly foreign tourists.

The men were alleged members of Jemaah Islamiyah (JI), a regional terrorist network responsible for several bombings across Indonesia in recent years.

Meanwhile, Amnesty International expressed deep disappointment by Indonesia's recent announcement that the Bali bombers will soon be executed, saying it represents a reversal of the global trend towards the abolition of the death penalty.

"While the Bali attacks were a horrific atrocity, Amnesty firmly believes that state-sanctioned killing will not bring redress for the victims, nor deter future criminal acts," Patrick Holmes, Amnesty's chief executive officer, said in a statement.

Amnesty called on Indonesia to commute all sentences of people awaiting execution, and to establish an "immediate moratorium against the death penalty," saying that the death penalty is the ultimate denial of human rights and opposes it in all cases without exception. (dpa)