2 variety -> scheme

I am looking for reference or hints how to prove the following result.

Let $G$ be a commutative $S$-group scheme which is the extension of an abelian variety scheme $A$ by a torus $T$. Then the n-torsion $G[n]$ is a finite flat $S$-group scheme.

Specifically, I have difficulties in showing that $G[n]$ is finite. For a general semi-abelian variety scheme we know that it is quasi-finite and flat, but not necessarily finite (see e.g. the book Neron Models, Lemma 7.3/2).

Let $G$ be a commutative $S$-group scheme which is the extension of an abelian variety $A$ by a torus $T$. Then the n-torsion $G[n]$ is a finite flat $S$-group scheme.
Specifically, I have difficulties in showing that $G[n]$ is finite. For a general semi-abelian variety we know that it is quasi-finite and flat, but not necessarily finite (see e.g. the book Neron Models, Lemma 7.3/2).