The blast that ripped through a wedding celebration in an Afghan village, killing 40 people, appears to have been aimed at 17 guests of an anti-Taliban guard group encouraged by the Americans.
The blast occurred late on Wednesday night in a housing compound in a Kandahar village where men had gathered during the wedding festivities, and children were among the dead and wounded.
The anti-Taliban guard organisation that was the likely target was initially encouraged by the American Special Operations Forces in the conflict-ridden nation.
The commander of the group, Mohammed Nabi Kako, said the village defense force is homegrown and home-financed, the New York Times said.
While the Americans supported the efforts initially, they never followed up with any assistance or ammunition.
"The Americans, they promised me that 'if you find the men, we will provide weapons and everything you need, vehicles, ammunition, radio,' then nothing happened," Kako was quoted as saying by the Times.
"When I asked why, they said, 'You should go to your government and your government will support you'".
Twelve out of the 17 men from the anti-Taliban group who were attending the wedding were killed.
Kako, however, expressed confidence about his operation.
"We will work harder against the Taliban in the future... Our morale is high, and our people's morale is even higher," he said.
Col Edward T Nye, a spokesman for Special Operations forces in Afghanistan, did not comment on the commander's remarks, according to the newspaper.
"This is not going to dissuade us or drive us away, and I'm sure we're going to continue to support the people of the area and side with them," he said.
The Karzai government has also not supported these groups because it might lead to the creation of power bases outside the capital.
"The local militia were quite effective and helpful and were supported by the civilian population; they were not letting Taliban come to their area," said Haji Shah Aka, an elder from Nagahan, according to the report.
The attack against civilians, which also injured 87 people, has been severely condemned.
"I am shocked and deeply saddened at the loss of life and large number of those injured last night in Nagahan village, Arghandab in Kandahar," Staffan de Mistura, the top UN official in Afghanistan said.