Lieutenant-Colonel Rumi Nielson-Green, a spokeswoman, said in the statement: "The coalition regrets the death of these non-combatants."
"We are planning to conduct a full and thorough investigation."
There has been a series of incidents in the past weeks in which civilians have been killed in international military action against the Taliban and other fighters trying to bring down the Western-backed government in Kabul.
On July 27, Canadian soldiers in the Nato-led International Security Assistance Force (Isaf) killed two children after opening fire on a car that did not slow down near a military patrol in the southern province of Kandahar.
The day before, Isaf troops killed four civilians in similar circumstances in neighbouring Helmand.
Also last month, the coalition admitted killing eight civilians in an air attack in the southwestern province of Farah.
The mounting civilian casualties in international military operations seven years after the US sent troops to Afghanistan to overthrow the Taliban government has angered Afghans.
The UN said in June that nearly 700 civilians had lost their lives in Afghanistan this year, about two-thirds in attacks by fighters and about 255 in military operations.
Afghan army increase
Robert Gates, the US defence secretary, has endorsed an Afghan government proposal to increase the size of the country's army by more than 50,000 troops.
|Observers say the Afghn army is unable to fight the Taliban alone [File: EPA]
The new plan will cost more than $10bn. Geoff Morrell, the Pentagon press secretary, said on Thursday that officials are currently looking at ways to finance it.
Options would include seeking money from Nato allies.
Morrell said the proposal would increase the size of the Afghan army from a planned 80,000 troops to roughly 122,000, as well as 13,000 in support staff.
In addition, Gates is to approve a plan that would give General David McKiernan broader control over US forces in Afghanistan.
McKiernan commands the Nato-led coalition in Afghanistan, which includes about 15,000 US forces.
Under the proposal, McKiernan would also control the additional US forces in Afghanistan who are training the Afghan army and police. There are about 33,000 US troops in Afghanistan, the highest since the war began in 2001.
"The US is looking to streamline the command and control by making McKiernan essentially in charge of all US forces in Afghanistan so that one person can deploy them in support of the overall mission," Morrell said
The Pentagon has long been considering military commanders' suggestions to better co-ordinate the mission in Afghanistan.