Equivalent of "du" utility in Unix or Sys module ?

In the ocaml interpreter, I can type 

Sys.command "du -d 1 pathformydirectory ";;

to inspect the disk usage in a given directory.

The problem is, the result is of type unit and I would prefer a result of type, say, (string*int) list.

 Is there a function from the Unix or Sys module that does this ?