The threat of annihilation by the death instinct within is, in my view — which differs from Freud’s on this point — the primordial anxiety, and it is the ego which, in the service of the life instinct — possibly even called into operation by the life instinct — deflects to some extent that threat outwards.
Klein explicitly identifies annihilation anxiety as the primordial anxiety, produced by the death instinct acting within and deflected outward by the earliest activity of the ego.
, Envy and Gratitude and Other Works 1946-1963, 1957thesis