A roadside bomb killed at least 12 people and wounded 26 in the western Afghan province of Herat on Monday, a security official said. A woman and child were among those killed in the blast and the district police chief was seriously wounded, security commander for Herat, General Esmatullah Alizai, said.The attack heightens concerns that the country's Taliban-led insurgency is spiking less than three weeks before landmark presidential and provincial council elections on August 20. Provincial police chief Esmatullah Alizai told reporters that the blast was caused by a bomb planted in a roadside rubbish bin. "It exploded as the convoy of district police passed by," he said. "Twelve people have been killed in this explosion and 20 other people have been wounded. Among those killed are two police." Another police officer had said the attack was caused by a suicide bomber. The blast hit the centre of Herat during the busy morning rush hour and an AFP reporter saw several police vehicles and private taxis damaged. Motorcycles and bicycles lay discarded at the site, and children's shoes and a woman's veil were left abandoned on the ground, he said. There was some police gunfire after the blast, the reporter said. The Taliban, who have vowed to disrupt this month's presidential election in Afghanistan, were behind the attack, a spokesman, Qari Mohammad Yousuf, said. The district police chief, Khoja Issa, was the target, he added.