What is the ruling on declaring the groups known as "Islamic groups" in Algeria to be disbelievers, and is it permissible to do so?

A declaration of disbelief (takfir) is a serious judgment with grave consequences in this life and the Hereafter. It is not pronounced except upon one who fulfills the conditions for takfir, by committing an act of disbelief that permits no interpretation, and in the absence of impediments such as coercion or ignorance. Extreme caution must be exercised in applying this term to Muslims, for he who says to his brother, "O disbeliever," then one of them has surely returned with it.