A roadside bomb ripped through a trailer packed with guests travelling to a wedding in southern Afghanistan, killing 21 civilians and wounding up to six others, officials said on Thursday.
The blast occurred in the southern province of Helmand on Wednesday, the interior ministry and the top Afghan commander for the south told AFP, correcting an earlier statement that the attack happened on Thursday.
"A trailer being towed by a tractor was hit by a roadside bomb... and killed 21 civilians and wounded six others," Afghan General Shir Mohammad Zazai said.
Afghan soldiers were dispatched to the area to help with rescue efforts.
"Among the killed there were also teenagers but we don't have exact figures now," Zazai told AFP.
It was one of the deadliest bombings in weeks and comes with Afghanistan buffeted by soaring insurgent attacks and suffering record levels of violence in the eight years since the 2001 US-led invasion ousted the Taliban regime.
The attack took place in Garmsir district, an insurgent stronghold where US Marines have for months been trying to flush out Islamist militants ahead of landmark presidential and provincial council elections on August 20.
In rural Afghanistan, where most people live in poverty without private vehicles, trailors are often harnessed to farm tractors to transport people.
"A tractor vehicle full of civilians was going to a wedding party in Garmsir district of Helmand province," the interior ministry told AFP.
"On the way the tractor was hit by an IED (improvised explosive device). As a result, 21 civilians, most of them children and women and young boys, were killed and five wounded," ministry spokesman Zemarai Bashary said.
It was too early to give a breakdown of the dead, he said, condemning what the ministry called an "inhuman and cruel attack of the terrorists" and calling on Afghans to help unmask "such bad elements who are trying to kill civilians".
There was no claim of responsibility for the attack.
Helmand is a Taliban stronghold and the militants rely heavily on bomb attacks in their campaign to drive out the Western-backed Afghan government and about 100,000 international troops deployed in the country.
President Hamid Karzai, who has ruled Afghanistan for nearly eight years, is the leading candidate in this month's presidential election.