With both presidential candidates declaring victory in Indonesia's knife-edge election this week, anxiety is growing that fraud and dirty tactics could twist official results due to be announced later this month.

Jakarta governor Joko Widodo and his rival, former general Prabowo Subianto, used different unofficial tallies Wednesday to claim victory in the world's third-biggest democracy.

Now more than 130 million ballot papers from the vast archipelago that sprawls the distance of London to New York are being counted and collected, and then sent on to the capital Jakarta. The official result will be announced by July 22.

Both camps have sent hundreds of thousands of monitors to watch the ballots' each and every move in a country where vote-buying and the bribing of government officials is rampant.

"The most vulnerable part of the Indonesian election is the counting process," Jakarta-based independent analyst Paul Rowland told AFP.

Analysts believe that Widodo, known by his nickname Jokowi and seen as a break from the autocratic Suharto era, has the more credible claim to victory, and as such is the most vulnerable to being targeted by such fraud.

At least eight polling agencies said he was leading Prabowo by between two and seven percentage points.

Most of these survey institutes have accurately predicted the results of Indonesian national elections since 2004, including April's parliamentary polls.

Prabowo, a top military figure in Suharto's time who has admitted ordering the abduction of democracy activists before the strongman's downfall, relied on data from four less well-known polling agencies.

Widodo has urged his supporters across the country to closely monitor the vote-counting process and ensure it is "honest and clean without intervention by any parties".

Rowland said that Widodo was "challenging the local election officials to make sure they don't accept money to change the numbers".

There has been no suggestion that his opponents have tried to carry out any fraud.

Hashim Djojohadikusumo, Prabowo's enormously wealthy brother who has helped bankroll his campaign, insisted that the ex-general also felt his campaign was under threat from Widodo's team.

"Frankly we are quite worried... our votes are being threatened," he said.

"We are not the only ones with money."


'Call for calm'

For transparency, votes are counted in public at polling stations, sometimes in front of large crowds and party witnesses.

The votes are tallied on a form visible to onlookers, then handed to village chiefs before being collected at a higher administrative level and eventually making their way to Jakarta.

Even after the result is announced by the election commission, the loser can challenge it, and analysts say both candidates will likely do so if they do not emerge the victor.

Any challenge will go to the Constitutional Court, which must declare a winner by August 24, ahead of the inauguration of a new president in October.

The worst-case scenario following a decision by the commission or court is violence breaking out. The country was plagued by unrest during its transition to democracy in the late 1990s, but has enjoyed more than a decade of peace and stability.

President Susilo Bambang Yudhoyono called both candidates to his residence outside the capital late Wednesday following their declarations of victory, and urged them to restrain their supporters from staging celebratory parades.

Both camps claim that polling agencies have taken sides.

The four main pollsters used by the Prabowo camp are little known and are coming under increased scrutiny, with the body that oversees pollsters in Indonesia reportedly raising concerns about their results.

But more reputable agencies too have vocally sided with Widodo. Rizal Sukma, executive director of Jakarta-based think-tank the Centre for Strategic and International Studies, has advised his campaign.

However, Aaron Connelly, a research fellow at the Sydney-based Lowy Institute for International Policy, said: "I think we can say pretty clearly the results used by Prabowo are not from respected polling firms.

"They are not particularly well established and they don't have track records of accuracy like others do."