* Incumbent President Koroma proclaimed victor on Friday
* Opposition claims "systematic and widespread irregularities"
* Fast-growing economy looks to iron ore, oil development
By Simon Akam
FREETOWN, Nov 24 (Reuters) - Sierra Leone's main opposition party on Saturday attacked the credibility of a poll that saw incumbent President Ernest Bai Koroma elected to a second term in an outright victory.
The dispute risks tarnishing a vote deemed free and fair by observers and that many hope will help pave the way for an economic revival of the war-scarred West African nation.
Koroma's main challenger Julius Maada Bio, a former military junta leader, said "systemic and widespread irregularities, malpractices and injustices ... undermined the credibility of the results."
While the SLPP stopped short of rejecting the results outright, a top party official said the chances it would accept its defeat when the party's leadership meets on Tuesday were slim.
"It's very unlikely. Our membership are very strong-hearted about it," the SLPP's national secretary general Banja Tejan-Sie told Reuters.
While analysts predicted ethnic loyalties would make it hard to secure the 55 percent of votes required for a first round victory in the Nov. 15 election, Koroma and his All People's Congress party won outright with 58.7 percent.
Bio garnered 37.4 percent of votes in a high turnout for the election, the third national poll since the end of a 1991-2002 civil war that made Sierra Leone notorious as a "blood diamonds" battleground for rebels and child soldiers.
At stake was the job of overseeing billions of dollars of investment in a natural resources boom with the potential to lift the gold, oil and iron-rich country from poverty.
Iron-ore shipments by British companies African Minerals and London Mining are expected to help the economy achieve 20 percent growth this year, below original forecasts of more than 50 percent, but still one of the highest growth rates on the planet.
While a large European Union observer mission said the advantage of incumbency meant the electoral playing field was skewed in favour of Koroma, it and other observers called the process free and fair.
More than 9,000 polling stations catered to the country of 5.5 million voters on election day.
In a statement released before the results on Friday, electoral commission chief Christiania Thorpe said recounts took place in 173 polling stations, however over-voting was only found to have occurred in five.
"It is mathematically impossible for the number of ballots in the ballot boxes to be recounted to impact the outcome of the presidential election," the statement read.
Koroma's spokesman Unisa Sesay said on Saturday that the poll result was credible and the NEC had thoroughly investigated the SLPP's complaints.
"It's not only Sierra Leoneans who are saying it," he said. "Don't forget that these are the elections that have been most comprehensively observed for a very long time."