WASHINGTON (Reuters) - Three African Islamist groups threatening to target Westerners have begun to cooperate among themselves, a "very worrying" trend that raises concern of a network stretching from Algeria to Nigeria, the top U.S. general for Africa said.

Other U.S. defense officials, speaking separately on condition of anonymity, agreed the African Islamist groups cooperate in sometimes alarming ways but played down the likelihood of an overarching grand alliance.

Read the complete story(Some news sites require registration)