The Afghan government is blaming the Taliban for the latest attack outside the southern city of Kandahar.
No one has claimed responsibility for the attack, which killed dozens of civilians, including women and children riding on the bus.
Afghan presidential spokesman Humayoon Hamedzada says authorities are investigating.
"We are deeply sorry for the loss of life, but our provincial authorities and the security agencies have received instructions to complete the investigations," Hamedzada said. Tuesday's explosion occurred just west of the city on a highway where a similar blast killed three civilians a day earlier. Late last week, the United Nations issued a report that said it had recorded some 1,500 civilian casualties between January and August. August was this year's deadliest month, as the Taliban sought to discourage people from voting in the presidential election. The report also said almost three times as many civilian deaths were attributed to anti-government elements than to pro-government forces.
The spokesman for international forces in Afghanistan, U.S. Army Colonel Wayne Shanks, says NATO troops are working with local populations to clear the roads of Taliban bombs.
"Every time [the Taliban kills] innocent civilians, they are hurting themselves," Shanks said. "Just like if we make a mistake and we hurt innocent civilians, we are hurting ourselves. And we are trying to absolutely fix that." Meanwhile in Pakistan, authorities say another suspected U.S. missile strike targeted militants in South Waziristan. Officials believe the insurgents in Pakistan's tribal regions have ties to the Taliban and al-Qaida and use the area as a base of operations for strikes in Afghanistan against foreign troops. Sean Maroney, VOA News, Islamabad
