KABUL : A US air strike in eastern Afghanistan has killed three civilians, the Afghan president’s office said on Tuesday.

The bombing took place in Khost on Monday night, a statement said. The US-led military coalition ISAF said it was looking into the incident. Air strikes that have killed or wounded hundreds of Afghan civilians are a serious source of tension between the two countries and one of the main reasons President Hamid Karzai has refused to sign an agreement that would allow US forces to stay beyond 2014. “The Afghan President called the strike a violation of agreements between the two countries and strongly condemned it,” the statement said. The Nato-led coalition declined to confirm whether there had been an air strike in the area overnight, saying only that it was looking into allegations of civilian casualties.

“We are looking into allegations of civilian casualties and we are assessing the circumstances,” said a spokesman in Kabul, Major Gary Allen. “I cannot even confirm the raid or air strike. We are trying to assess what exactly did happen.” Heavy publicity around air strikes that have killed civilians in Afghanistan have sometimes meant that other types of explosions have been mistaken for such incidents. A small number of US and Nato forces are expected to stay on to help train Afghan soldiers and possibly target groups like al-Qaida in lawless parts of the country, but Obama has said they will not be involved in the domestic fight against Taliban insurgents.