JAKARTA – The World Bank delivered a blunt assessment of Indonesia ban on mineral ore exports onTuesday, warning that it would hit trade and government revenueand risked undermining already weak investor sentiment towardsSoutheast Asia's biggest economy.Implemented in January, five years after the law wasinitially passed, the ban has been met with confusion in themining sector.It was introduced to encourage mineral processing inIndonesia in order to increase the value of exports. But, onegroup of mining companies has mounted a legal challenge, warningthat the ban on exports will force them out of business."The long term gains are at best uncertain," Jakarta-basedWorld Bank economist Jim Brumby said, adding there were nosuccess stories elsewhere in the world where countries had triedto impose similar bans.Brumby was speaking at the launch of the Bank's quarterlyeconomic report.The World Bank estimated that for the period 2014-2017, thenegative impact on net trade could be $12.5 billion because ofthe loss of export revenue while capital goods imports, to buildsmelting capacity, will have to rise.The potential cost in lost fiscal revenues, includingroyalties and export tax, could be $6.5 billion.And if a proposed major nickel mining and smelting projectin Weda Bay in the east of the country does not kick in by then,the negative impact will go beyond 2017.None of the major parties contesting next month'sparliamentary election and the presidential election in Julyhave suggested they would repeal the law, though some have saidthat they would review its implementation.Indeed, all the main parties agree Indonesia should do moreto make its exports more valuable.Economic nationalism has become more evident in Indonesianpolitics thanks in part to self-confidence arising from astrengthening domestic economy. There is a popular belief thatforeign investors profit too much from exploiting the country'senormous wealth of natural resources.The ban has increased policy uncertainty, weakening theinvestment climate for mining in Indonesia, when it was alreadyseen as one of the world's weakest, the World Bank report said."Over the longer term, this could prove to be the biggestobstacle in increasing domestic value-addition, as it increasesinvestor risk perceptions at a time when economy-wide investmenthas already decelerated," the report said.It urged deeper analysis and wider consultation on theissue.