Afghan policemen secure the site at the main checkpoint leading to the Interior Ministry, after a suicide bomb blast in Kabul.KABUL, April 2 (Reuters) - A Taliban suicide bomber blew himself outside Afghanistan's interior ministry in central Kabul on Wednesday, killing himself and at least six policemen, the latest in a string of attacks ahead of Afghanistan's April 5 presidential election.Taliban insurgents also killed nine civilians including a provincial council candidate in northern Afghanistan, local officials said.The Islamist Taliban have promised to do everything in their power to disrupt the April 5 vote when Afghans elect a successor to the incumbent president, Hamid Karzai, who is barred by the constitution from running again.The Kabul attack came on the last day of campaigning for an election that is intended to mark the first democratic transfer of power in Afghanistan's history."A suicide bomber wearing a military uniform ... detonated his explosives at the main gate of the interior ministry," the ministry said in a statement."As soon as the bomber saw some policemen he detonated his explosives. It was impossible for him to enter the facility with the suicide vest," a ministry spokesman added.The Taliban claimed responsibility for the attack in an e-mail, saying the bomber had penetrated a third ring of security at the ministry before setting off the blast.The Taliban have stepped up the pace of attacks in the run-up to the vote, targeting those organising the election and foreigners, but campaign rallies have been largely undisturbed.In the northern province of Sar-e-Pul, militants shot dead nine people, including provincial council candidate Hussain Nazari, after kidnapping them two days ago, officials said."They were travelling from Balkhab district to central Sar-e-Pul to attend a campaign two days ago but the Taliban kidnapped them," Abdul Jabar Haqbeen, governor of Sar-e-Pul, told Reuters."Last night our security forces found nine dead bodies separately in areas between Balkhab and Sar-e-Pul. All were shot by the Taliban. One person was found seriously wounded."Global powers are closely watching the election which comes at a crucial time in Afghanistan as most foreign troops prepare to pull out.In a separate statement, the Taliban warned voters against participating in what they described as a "fake election process"."The Islamic Emirates announces one last time that all elements of the fake elections will be under our Mujahideen attack," they said in a statement."Every official and every voting centre will be in danger and a surge of attacks will start all over the country."(Reporting by Mirwais Harooni in Kabul and Bashir Ansari in Mazar-I-Sharif; Writing by John Chalmers; Editing by Nick Macfie and Simon Cameron-Moore)Suicide bomber kills six police at Afghan ministry ahead of voteReuters: Ahmad MasoodAn Afghan policeman takes up a position at the main checkpoint leading to the Interior Ministry, after a suicide bomb blast in Kabul April 2, 2014. The suicide bomber blew himself up outside the Afghan interior ministry building in the centre of Kabul on Wednesday, wounding several police officers, the ministry said in a statement. Getty Images: Aldo Solimano, AFPA man stands among sunken fishing boats April 2, 2014, at the