Afghanistan says U.S. air strike kills three civilians --- (Reuters) - A U.S. 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 U.S.-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 U.S. 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. - More, at: http://www.reuters.com/article/2014/04/15/us-afghanistanblast-idUSBREA3E17L20140415