Jakarta  - Indonesia's General Elections commission on Saturday declared President Susilo Bambang Yudhoyono the winner of this month's presidential election, but his rivals vowed to challenge the conduct of the polls, citing irregularities in the voter rolls.

Yudhoyono won the July 8 election with 60.8 per cent of the vote, said Andi Nurpati, a commission member who announced the final official vote tabulations.

His rivals, former president Megawati Sukarnoputri and outgoing Vice President Jusuf Kalla, had 26.8 per cent and 12.4 per cent of the vote, respectively.

Yudhoyono's landslide victory meant there was no need for a run-off.

Yudhoyono and Kalla signed the vote tabulation documents at the commission's headquarters, where police barricades had been erected and armored vehicles were on standby in case of violent protests by rival supporters.

But Megawati refused to appear in protest of what her campaign team called "legal flaws" in the conduct of the election.

A spokesman for Kalla's campaign team, Burhanuddin Napitupulu, said it would file a suit at the Constitutional Court Monday, saying there had been irregularities in the voter rolls, including duplicate names, that had prevented millions from casting their ballots.

"We accept the results but not the process," he said.

A lawyer for Megawati, Gayus Lumbuun, said her campaign team would also challenge the results at the Constitutional Court for similar reasons.

Independent experts have criticized the election commission for failing to address problems in the voter list.

If legal challenges mounted by opposing candidates fail, Yudhoyono would be installed as president for a second, five-year term on October 20.

More than 176 million people were registered as eligible voters but nearly 50 million of them did not vote, the commission said.

Yudhoyono, 59, has been credited with some successes in his first term, including stabilizing the economy, cracking down on deep-rooted graft and bringing peace to the rebellious Aceh province.

Analysts said his resounding victory gives him a stronger mandate to pick professionals for his next cabinet and push through reforms as he faces the daunting task of tackling the effects of the global economic crisis.

Last week's bombings at two luxury hotels in Jakarta, which killed nine people including two suspected suicide bombers, have raised fears of a return of instability to the world's most populous Muslim nation after a few years of calm.

Police suspect the attacks were the work of Islamic extremists linked to Jemaah Islamiyah, a militant group that has been blamed for a string of previous deadly bombings in Indonesia.

Experts hailed this month's peaceful election as an indication of how Indonesia has come a long way since the turmoil that marked former dictator Suharto's departure in 1998.

A decade ago, South-East Asia's largest economy was a shambles, being hard hit by the region's 1997-98 financial crisis.

Until a few years ago, Indonesia still grappled with a separatist insurgency in Aceh and Muslim-Christian violence in the east of the country. (dpa)