At least 30 civilians travelling on a bus in southern Afghanistan have been killed by a roadside bomb blast, the Afghan interior ministry has said.
The bus was on its way from Herat to Kandahar when the device exploded, the ministry said, adding that 10 children and seven women were among the dead.
The most seriously wounded have been taken to a Nato base for treatment.
Kandahar's provincial government blamed the Taliban for planting the device, although the group has yet to comment.
A similar blast on the same main road - in Maywand district - had killed three civilians on Monday, a government spokesman said.
"An explosion hit the bus. I don't know what happened. When I came to, I got out of the bus and saw that it was totally wrecked," one of the passengers, Lal Jan, told the Associated Press in Kandahar.
The BBC's Martin Patience in Kabul says the Taliban are increasingly using roadside bombs to attack foreign forces.
However, civilians are frequently caught up in the violence, our correspondent says. According to the UN, more than 1,500 have been killed this year, the majority in insurgent attacks.
'More troops needed'
The deaths come shortly after Anders Fogh Rasmussen made his first speech in the United States as Nato secretary-general.
Speaking at the Atlantic Council in Washington, the former Danish prime minister called on European nations to stand with US forces in Afghanistan.
There are currently some 100,000 foreign soldiers in Afghanistan from more than 40 countries - more than 60,000 of them American.
US military commanders have warned that more troops will be needed, but US President Barack Obama says he will not decide until after a strategy review.
The commanding US officer in Afghanistan, Gen Stanley McChrystal, delivered a review of the situation in the country to Mr Obama earlier this month.
However, rising military casualties have undermined public support for the operation in some Western countries.
Correspondents say European nations are not expected to offer any significant increase in troops unless Washington takes the lead.
The Netherlands and Canada have already set 2010 and 2011 as deadlines for withdrawal and Italy has announced plans for a "strong reduction" in its forces.