Frances makes a good point. It very much depends on what you are doing when you say this.
If, for example, you are entering a room where people (e.g. students or office workers) are working and they look up to see who has entered... you could say "Sorry for the interruption. Please continue working." or "please carry on with your work". It must be said that you would only say this if you are in a position of some authority (e.g. a teacher or principal wanting to talk the teacher of the class or a manager wanting to talk to talk to the supervisor or simply to observe the work.) That is, you can only say it if you have the authority to tell them what to do.
Now, if you are interrupting a co-worker to ask a question, as you are leaving you can say what Su Ki suggested "Sorry to have bothered you. I'll let you get back to your work now." or "I'll let you get on with your work now." In this situation, you don't have the authority to tell your co-worker what to do; you are just saying that you will stop bothering him/her (at least for now).