The US military says airstrikes by a US bomber in Afghanistan last month did not follow strict rules and probably caused civilian casualties. The military said an estimated 26 Afghan civilians died in the May 4 incident. It is most likely that the deaths occurred during three bombing runs by a B-1 bomber. Those were the conclusions of a report issued Friday after a lengthy investigation. The military report said it was impossible to know for sure how many civilians died and did not rule out that the number could have been higher. Afghan officials have said as many as 140 people were killed.