grammar - Dropping of "was" from "A couple of ministers had to resign too, among them [was] Interior Minister Fouchet."

A couple of ministers had to resign too, among them Interior Minister
Fouchet.

I don't know what type of rule is used to delete needed "was" in this sentence. My opinion is that "was" should be used like this.

A couple of ministers had to resign too, (and) among them was
Interior Minister Fouchet.

Can someone tell me what rule is used to delete "was"? For example, be deletion, appositive, whiz deletion or etc?