At least two policemen and election workers were killed, several others wounded on Monday, when a motorcycle bomb went off in western Herat province of Afghanistan, said officials.The provincial Police Chief Brig. Gen. Samiullah Qatra said in a press statement that the explosion occurred in Rubat Sangi district killing four people and wounding four policemen and many civilians. He further told that the blast took place when a campaign rally for presidential runner Dr. Abdulla Abdullah was ongoing near his campaign office.The office of the presidential runner confirmed that bomb-rigged motorcycle exploded in front of presidential candidate Dr. Abdullah Abdullah's campaign office, where a gathering was ongoing. The office condemned in a statement the attack and urged security forces to tighten security measures around campaign offices, due to efforts at disrupting political activities had increased. The presidential elections in Afghanistan are scheduled to be held on April 5, giving a rise to the number violent incidents in the country. The Taliban rebels on Monday warned that they would disrupt the elections and asked the Afghans to stay away from the ballot, said local media reports.