A powerful early morning suicide truck bomb devastated a hospital in southern Afghanistan on Thursday, killing at least 20 people and wounding more than 90 others, an official said. The Taliban took responsibility for the attack, which destroyed part of the hospital in Qalat, the capital of southern Zabul province, and left a fleet of ambulances broken and battered. Residents, many of whom had come to see their sick family members, used shawls and blankets to carry the wounded inside the destroyed building, while authorities scrambled to take the worst of the wounded to hospitals in nearby Kandahar. "The bomb was huge and it was carried by a mini-truck," said a senior defence ministry official in the capital, Kabul, speaking on condition of anonymity as he was not authorised to speak to media. The militants meant to target a training base for Afghanistan's powerful National Directorate of Security, but parked the vehicle laden with explosives outside a hospital gate nearby, said another defence ministry source. In the hours after the explosion there were contradictory figures of the dead and wounded. The provincial governor's spokesman Gul Islam Seyal put the death toll at 12 but said authorities were on the scene sifting through the debris. Atta Jan Haqbayan, head of the provincial council, put the death toll at 20. Mr Haqbayan said the wall of the National Security Department (NDS) building was damaged. He couldn't say whether any personnel were among the casualties. The Taliban, who have been carrying out nearly daily attacks since peace talks with the United States collapsed earlier this month, said the target was a nearby government intelligence department building. The Taliban has warned that its fighters will step up their campaign against the Afghan government and foreign forces to dissuade people from voting in the September 28 election. More than 9 million Afghans are expected to vote in the presidential election, during which the government has committed more than 70,000 security forces across Afghanistan to protection duties. US President Donald Trump abruptly ended talks this month with the Taliban for a deal on the withdrawal of thousands of American troops from Afghanistan, in exchange for security guarantees from the hardline Islamist group. The talks, which did not include the Afghan government, were intended to lead to wider peace negotiations to end the 18-year-long war in Afghanistan. US Afghanistan envoy Zalmay Khalilzad will testify on about the negotiations behind closed doors to Congress on Thursday. The House of Representatives' Foreign Affairs Committee issued a subpoena to force Mr Khalilzad to appear after it complained about being kept in the dark over the negotiating process. "We have reached an accommodation... to hear from Ambassador Khalilzad in a classified briefing," Eliot Engel, the committee chairman, said in a statement on Wednesday, adding the subpoena had been withdrawn. "While I would have preferred to hear from Ambassador Khalilzad in an open setting, I'm glad our members will have this long overdue opportunity to press for answers on the peace plan."