KABUL (Reuters) - Concerns over security and transparency in Afghanistans parliamentary election grew on Friday after another candidate was attacked and a German observer sought to temper expectations of the poll. The Sept 18 vote is seen as a litmus test for stability, as well as a test of the credibility of Afghan President Hamid Karzai after a fraud-marred presidential poll last year. In the latest attack, a candidate was wounded in a grenade attack in Ghazni city, southwest of Kabul, on Thursday, the Nato-led International Security Assistance Force (ISAF) said. The candidate, Moulana Abdul Rahman, and an Afghan civilian were wounded when the grenade was thrown in the governors compound in Ghazni. At least four candidates have been killed and at least 15 campaign workers and supporters have been wounded in recent weeks, raising doubts about whether Afghan forces will be able to secure the poll adequately despite the presence of almost 150,000 foreign troops in Afghanistan. Afghanistans Independent Election Commission has said more than 930 polling centres, out of a total of 6,835, would not open because of security concerns. About 2,500 candidates are running for 249 seats in the Wolesi Jirga, or lower house of parliament, in Afghanistans second parliamentary vote since the Taliban were ousted. More than a third of ballots cast for Karzai in last years presidential vote were thrown out as fake and some observers have already warned that this years vote also wont be trouble-free. It will be difficult, Germanys special representative for Afghanistan, Michael Steiner, told reporters in Berlin. We shouldnt fool ourselves - standards will not be on a level with Europe. Its more about reinforcing the mechanism.