KABUL (AFP) - US-led Nato forces in Afghanistan on Friday apologised for an air strike that President Hamid Karzai said killed a two-year-old boy, as acrimony deepened over a deal to allow US troops to stay in the country after 2014.
Civilian casualties have been one of the most sensitive issues of the 12-year military intervention in Afghanistan, and Mr Karzai warned that the latest incident threatened the proposed bilateral security agreement (BSA) with Washington.
An official from Nato's International Security Assistance Force (ISAF) said that force commander General Joseph Dunford "quickly called President Karzai and expressed deep regrets for the incident".
"We did not target or strike a house. The information that we have shows that the air strike hit the road," the ISAF official said. "Unfortunately, the civilian victims were in the vicinity of the strike."
Gen Dunford told Mr Karzai he was committed to a joint investigation into the attack, which ISAF said targeted a Taleban commander involved in operations against Afghan security forces in the southern province of Helmand.
Mr Karzai, whose troubled relationship with the US erupted again in public last week over the security deal negotiations, has often used civilian deaths caused by Nato to berate the international coalition for its failures in Afghanistan.
Mr Karzai "strongly condemns the air strike by Nato forces on a house which killed one child and wounded two women", a statement from his office said.
"This attack shows American forces are not respecting Afghan lives... As long as unilateral acts and atrocities continue by American forces on our people, we won't sign this BSA."
The strike was launched from an unmanned drone and hit the village of Faqiran in Helmand on Thursday morning, the statement said.
ISAF said that the strike targeted an insurgent riding a motorbike but did not confirm that a drone was involved.
Mr Karzai's spokesman Aimal Faizi further stoked tensions by saying that President Barack Obama had broken a recent promise "to respect the sanctity and dignity" of Afghan civilians in the same manner as US citizens.
"That is how the US respects the sanctity and dignity of homes in the US, bombing a residence for an individual?" Mr Faizi said in an e-mail to AFP.
"It is just another example of not fulfilling the commitments of the past."
Mr Karzai, who is due to step down ahead of presidential elections in April, has been stalling over the security pact that would see some US troops to remain in Afghanistan after next year for training and counter-terror missions.
About 75,000 Nato combat troops still deployed in Afghanistan are due to withdraw by the end of 2014 after fighting the Taleban since the Islamists were forced from power in 2001.
Helmand provincial spokesman Omar Zwak told AFP that Thursday's air strike had killed a child called Rafiullah and that a second drone attack killed the targeted commander.
The US has stressed that the BSA cannot be delayed further as Nato combat forces plan their withdrawal, and warned that vital international aid was at risk due to the extended postponements.
Mr Karzai last week refused to sign the BSA promptly despite a "loya jirga" assembly that he convened voting for him to do so, and he has since raised new conditions with US negotiators - provoking frustration in Washington.
"We very much welcome the conclusions of the loya jirga," US ambassador James Cunningham said on Wednesday in the western Afghan city of Herat.
"We have a good agreement and we're prepared to sign it in the near future."
A similar US deal with Iraq collapsed in 2011 leading to a complete US troop pull-out and the country is now in the grip of savage sectarian violence.
Analysts say Mr Karzai is keen to secure a reputation as a strong nationalist leader who stood up to foreign powers before he leaves office, even at the risk of alienating Afghanistan's biggest aid donor.