Sixteen Afghans including women and children were killed in their homes by a rogue US soldier in a pre-dawn rampage yesterday, plunging relations between the two countries into a new crisis.

...there is a risk of anti-American feelings and protests in coming days

Afghan President Hamid Karzai condemned the slaughter as “unforgivable”. “When Afghan people are killed deliberately by US forces this action is murder and terror and an unforgivable action,” Mr Karzai said in statement.

US President Barack Obama said he was “deeply saddened” at the shooting spree in Afghanistan.

“I offer my condolences to the families and loved ones of those who lost their lives, and to the people of Afghanistan, who have endured too much violence and suffering,” Mr Obama said in a written statement, describing the incident as “tragic and shocking”.

The American soldier entered the homes of civilians in the southern Kandahar province and killed 16 people including nine children and three women, the statement said.

It quoted a wounded 16-year-old, who was shot in the leg, as telling Mr Karzai by phone that the US soldier entered their home in the dark, woke up his family members and thenshot them.

“The government and the people of Afghanistan demand an explanation from the US government of this incident,” Mr Karzai said.

US Defence Secretary Leon Panetta assured Mr Karzai in a phone call that a “full investigation” was under way. “A suspect is in custody, and I gave President Karzai my assurances that we will bring those responsible to justice,” Mr Panetta said.

Nato’s International Security Assistance Force said it had arrested a soldier over the incident, and the commander, General John Allen, condemned “this deeply appalling incident”.He also vowed to hold “fully accountable” anyone found responsible for the killing spree.

“I cannot explain the motivation behind such callous acts, but they were in no way part of authorised ISAF military activity,” his deputy, Lt Gen. Adrian Bradshaw, said.

The US embassy in Kabul sent out an alert to its citizens in Afghanistan warning that as a result of the shooting “there is a risk of anti-American feelings and protests in coming days”.

Sources said the rampage began after a US soldier walked off his base in the early hours of yesterday morning, apparently heavily-armed and carrying night-vision equipment. He was arrested outside the base after the shooting by members of the Afghan National Army.