By Kuratowski's theorem, every nonplanar graph contains a (topological) minor of $K_5$ or $K_{3,3}$.<br>
But I observed that every time I construct a $4$-connected nonplanar graph, it always contains not only a $K_{3,3}$-minor but also a $K_5$-minor.<br>
Moreover, although I tried many times, I cannot construct a $4$-connected nonplanar graph containing only $K_{3,3}$-minors!<br>
So I want to know whether the following statement is true:
>Every $4$-connected nonplanar graph contains a $K_5$-minor.

Unfortunately, I could not find any references about this topic.<br>
If the statement is true, can you give me a proof?<br>
Or if it's not, can you show me a counterexample?<br>
Thanks a lot.