The US military in Afghanistan has revealed that six children died in a raid on suspected militants in the eastern province of Paktia last week.
The US says civilian casualties are inevitable
News of the deaths came shortly after the US apologised for killing nine children in a separate raid in the neighbouring province of Ghazni.
However, the US has warned it will not be deterred by civilian casualties.
Afghan President Hamid Karzai has sent investigators to Ghazni amid concern the raids are alienating local people.
A US spokesman, Lieutenant Colonel Bryan Hilferty, told reporters in Kabul on Wednesday that the bodies of six children were found under a collapsed wall at a compound 20 kilometres (12 miles) east of Gardez, in Paktia province.
Two adults' bodies were also found at the scene when ground forces searched the area on Saturday.
The US spokesman said there had been no indication that civilians were at the scene and he suggested the victims were partly to blame for being at a site used by militants to store munitions.
"If non-combatants surround
themselves with thousands of weapons and hundreds of rounds of ammunition and howitzers and mortars, in a compound known to be used by a terrorist, we are not completely responsible for the consequences," he said.
The raid was launched in the belief that a suspected militant, Mullah Jilani, was staying in the compound.
When troops arrived they did not find the suspect but made nine other arrests, a US spokesman said.
US Defence Secretary Donald Rumsfeld has defended the aggressive pursuit of militant leaders in Afghanistan, saying
the Pentagon is equally happy to capture or kill them.
The US military earlier admitted mistakenly killing nine children in an air attack on Saturday against another suspected militant in Ghazni Province.
"I can't guarantee that we will not injure more civilians," said Lieutenant Colonel Hilferty, adding: "I wish I could".
Dec 2001: 65 killed in bombing of convoy of tribal elders
April 2002: Four Canadian soldiers killed
July 2002: 48 killed when bomb hits wedding party
April 2003: 11 killed by bomb in village of Shkin
Dec 2003: Nine children killed by bombing in Ghazni Province; six children killed in raid in Paktia province
*Mistakes accepted by US
During the Ghazni raid, an A-10 ground attack aircraft opened fire at a figure thought to be that of a militant leader, Mullah Wazir.
The identity of the man killed along with the children has been disputed.
Villagers say he was a local labourer and that the intended target had left the area days before the attack.
General Richard Myers, the chairman of the US Joint Chiefs of Staff, was among senior US figures to offer condolences after Saturday's deaths.
"We haven't been perfect," he said.
'This is not helping'
Afghan officials have warned that "mistakes" such as the Ghazni deaths risk undermining the US-backed Afghan Government.
Hamid Karzai said on Wednesday he had sent his own investigators to Ghazni but the president, a key US ally, was careful not to apportion blame.
"We are trying to find... the best possible manner to prevent incidents like that," he said.
"We are thinking if aerial activity is helpful or if it causes suffering."
Nazir Saberi, a minister in the Afghan Government,
told the BBC's Newshour programme that he was "angry at the people who are not being very, very careful about these things".
He said that coalition forces had to "learn to coordinate with the Afghan authorities".
"This is not helping really the government... and people will be angry and everybody is embarrassed like myself," he added.
"It is terrible, the tragedy of children being killed."