NATO has acknowledged that coalition and Afghan troops killed a number of civilians during an operation in eastern Afghanistan, saying it deeply regrets the loss of life. Alliance officials said, a complete casualty toll is uncertain, but at least four, and possibly as many as a dozen of more civilians died before dawn yesterday in Nangahar province. Local officials said, at least 26 civilians were killed during two separate incidents. President Hamid Karzai has ordered a investigation.