KABUL (Reuters) - Afghanistans Taliban said on Sunday they would attempt to disrupt elections this month and warned Afghans to boycott the vote, the first explicit threat against the poll by the insurgents. The September 18 parliamentary election is seen as a litmus test of stability in Afghanistan before US President Barack Obama conducts a war strategy review in December that will examine the pace and scale of American troops withdrawal from July 2011. This (poll) is a foreign process for the sake of further occupation of Afghanistan and we are asking the Afghan nation to boycott it, Taliban spokesman Zabihullah Mujahid said. We are against it and will try with the best of our ability to block it. Our first targets will be the foreign forces and next the Afghan ones, he told Reuters by telephone from an undisclosed location. Nader Nadery, Chairman of the independent Free and Fair Election Foundation of Afghanistan, said the threat was worrying because it could lead to poor voter turnout in the ethnic Pashtun belt in the south, where the Taliban are strongest. The people know that when the Taliban warn, they deliver on those warnings, and that prevents people from engaging very actively, Nadery said. The Taliban launched about 130 attacks against last years poll. They failed to disrupt it in much of the country, but in the Pashtun south turnout was low, observers were kept away and fraud was rampant. Abdullah Abdullah, a former foreign minister who came second behind Karzai last year, said he was worried about security. Not only has it not improved in the last few months, it has deteriorated, Abdullah told a news conference in Kabul. According to Afghanistans Independent Election Commission (IEC), 938 out of a planned 6,835 polling centres will not open on election day because of security fears. The United Nations said in a statement on Sunday it agreed with that decision to protect the security of voters, electoral workers and the secure and effective scrutiny of polling centres and voting procedures. The UN-backed Electoral Complaints Commission (ECC) said it was concerned some public officials were using their positions to help certain unidentified candidates and urged the government to protect the polls impartiality and integrity. The Commission said on Sunday 76 candidates had been disqualified so far for a range of reasons, from improper registration to links with warlords and private militias. 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.