A suicide bomber drove an explosives-packed Humvee into a police compound in Afghanistan on Friday, killing at least six officers a day after US Vice President Mike Pence said "real progress" is being made on the ground in the country. The Taliban claimed responsibility for the pre-dawn attack on the Maiwand district police headquarters in the southern province of Kandahar. It was the latest deadly assault by the insurgents, who have been increasingly targeting security installations. The vehicle was carrying an estimated 3,000 kilograms of explosives, Maiwand district police chief Sultan Mohammad told AFP -- roughly twice the number of explosives used in a massive truck bomb in Kabul in May which killed around 150 people.  "Our latest toll shows that we have six police officers martyred and five wounded," Mohammad said, adding the figures could change.  Kandahar police spokesman Ghorzang Afridi confirmed the death toll.  "All the victims were local policemen," Afridi told AFP. While Afghan officials routinely understate the casualty toll in attacks carried out by insurgents, it appears the attacker failed to reach the building where a large number of police were deployed. Mohammad said the attacker got through the first checkpoint and then detonated the vehicle at the second security check after a policeman opened fire. One building "was completely destroyed and two other buildings next to it were damaged too," he said.  The force of the blast also blew out the windows of shops located two kilometers away, he added. "The explosion was very loud and you could hear the sound of the blast miles away from the headquarters," a local police officer told AFP on the condition of anonymity. He put the death toll at eight with nine others wounded.  "The eight policemen who were killed have been removed or pulled out from under the rubble, and there were other policemen who went missing following the attack," the officer said.  Pence told US troops in Afghanistan Thursday that they have put the Taliban on the run, as he became the most senior Trump administration official to visit the men and women fighting Americas longest-ever war. Flying secretly through the day and night on a standard unmarked US Air Force C-17, Pence corkscrewed into Bagram Airfield on the unannounced visit, to thank some of the roughly 15,000 US personnel still hoping to turn the tide in the conflict, now in its 17th year. "The American people deserve to know that with the courage of everyone gathered here, were making real progress in this fight for freedom in Afghanistan," Pence told the troops. "Weve dramatically increased American air strikes. And together with our Afghan partners, weve put the Taliban on the defensive," he said, also pointing at efforts to target the drug trafficking networks that help fund the Taliban.