iOS - Best way run repeated task while app is active

iOS - Best way run repeated task while app is active

I want to run a task in the background while app is active and running.
The task should be executed repeatedly in every 2 minutes or so. If the
application is inactive then the 'background repeated task' should be
paused and it should continue if the app is active again. What is the best
way to do this ? Please help.