KABUL (AFP) - A wave of bomb blasts and shootings killed 32 people, including two children, in Afghanistan Monday as President Hamid Karzai jetted to Washington for a summit on defeating extremism. In the bloodiest incident a bomb tore through a tractor and trailer transporting a group of Kuchi nomads in a remote district of southern Zabul province, a district governor said. A roadside bomb struck their vehicle and killed 12 people, said Wazir Mohammad, head of the Shamalzai district on the border with Pakistan. The dead were six women, two children and four men, he said. There was no claim of responsibility for the blast but there are regular bombings in Afghanistan, most of them blamed on Taliban fighters targeting Afghan and foreign security forces. Mohammad also said two Taliban fighters were killed in the same district early Monday when mines they were planting in a road exploded. Taliban fighters elsewhere attacked a construction site near the Zabul capital, Qalat, where labourers were rebuilding bridges destroyed in earlier militant action, deputy provincial police chief Ghulam Jialani said. Six security guards protecting the workers were killed in the shoot-out, along with two civilian passers-by, he said. In the eastern province of Laghman, a suicide attacker walked up to a vehicle carrying the provincial mayor and blew himself up, killing the official and six other people, the interior ministry said in a statement. A spokesman for the Taliban, Zabihullah Mujahid, said his group was responsible. The mayor of Laghman, Mohammad Rahim Rahim, was one of the most senior officials in the province after the governor. The mayor, three of his bodyguards and three civilians were martyred, the ministry said. In western Farah province meanwhile, three policemen were killed and three wounded in a firefight with Taliban, police said. A big number of militants have also been killed but we cannot give a figure now, provincial police chief Abdul Ghafar Watandar told AFP. Authorities in the western province of Herat also reported that 13 Taliban and a policeman were killed in clashes in the area Sunday. Karzai headed to Washington Monday to meet US President Barack Obama and Pakistan President Asif Ali Zardari amid concerns about efforts to fight the Al-Qaeda and Taliban-linked threat in the region.