Yes, You Can.
In order to show the interaction among the modules sequence diagrams can be used. But the classes that will be used in the sequence diagram must be proxy classes.


In RUP the term "proxy class" is used to represent the class which provides a way to define the interaction of other modules (subsystem's) to a subsystem.
Means, create a proxy class and that represent a module (subsystem) and use it in ur interaction diagram to show the messaging with other modules.