How to add jar dependency during ant build

Hi

          In our project we are using ant script for automatic build. Our project having some jar dependency. That jar placed in specific folder and that path hard coded in ant script.
     If i execute this ant script using ant tool then not having any issue but when i use this same ant script with teamcity then it giving me class not found error(These all classes from
     that dependency jar file). Plz can one tell me how to add jar dependency in ant script with teamcity.