Franz Rauchenstein, head of the International Committee of the Red Cross (ICRC) delegation in Kabul, said: "We call on all parties to the conflict, in the conduct of their military operations, to distinguish at all times between civilians and fighters and to take constant care to spare civilians.
"Civilians must never be the target of an attack, unless they take a direct part in the fighting."
The inquiry into Sunday's incident in Nangarhar, however, raises tensions between the Afghan government and foreign troops based in the country, whose mandate is to support the Afghan authorities.
In the past, President Hamid Karzai has said that no civilian casualties are acceptable.
Some local politicians have demanded that charges be brought against those responsible for Sunday's air strike.
"The Americans say they can't miss a target of four inches," said Burhanullah Shinwari, the head of the investigating team, who is also deputy speaker of the Afghan senate.
"With all their technological advances, how can they not differentiate between a wedding party, women, children and the Taleban and al-Qaeda?"
They are also calling for the families to receive compensation, or blood money, which is common in Afghanistan.
While international forces do sometimes pay compensation, critics say that the process is not transparent, and more often than not families are left with no answers to why the victims were killed and no money.
Civilian casualties are caused by three main players in Afghanistan - the Taleban, international forces, and the Afghan army and police.
According to the Nato-led International Security Assistance Force (Isaf), more than 350 civilians have been killed and 800 wounded in Taleban attacks this year, with most victims caught in suicide bombings often aimed at foreign troops.
An Isaf spokesman would only say that the number of civilians killed in Isaf operations were in the "low double figures".
But a number of local organisations say the true number is far higher.
Foreign troops have been the targets of frequent attacks by militants
Public perception matters greatly to the international forces, particularly as they say they are waging a "hearts and minds" campaign.
The UN Assistance Mission in Afghanistan (Unama) posed this question on its website: "Who do you think causes the most civilian deaths in the country?"
Of the 149 votes cast so far, 70% said the Taleban and other insurgents, 24% said international military forces, while 6% said Afghan security forces.
Military officials say that while extremely regrettable, civilian casualties are inevitable in war zones and that many parts of Afghanistan are either regularly attacked by suicide bombers or gripped by an insurgency.
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