Abstract Let $G$ be a finite group, with a finite operator group $A$,
satisfying the following conditions:
(1)~$(\vert G \vert, \vert A \vert)=1$;
(2)~there exists a natural number $m$ such that for any $ \alpha,
\beta \in A^{\sharp}$ we have:
$[\,C_G(\alpha),\underbrace{C_G(\beta),\dots,C_G(\beta)}_{m}\,]=\{1\}$;
(3)~$A$ is not cyclic. We prove the following:
(1)~If the exponent $n$
of $A$ is square-free, then $G$ is nilpotent and its class is
bounded by a function depending only on $m$ and $\lambda(n)$ ($=n$).
(2)~If $Z(A)=\{1\}$ and
$A$ has exponent $n$, then $G$ is nilpotent and its class is
bounded by a function depending only on $m$ and $\lambda(n)$.
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