Hi Neeraj,
Looks like you might want to post your question on the users' list
(you posted to the developers' list):
https://www.libreoffice.org/get-help/mailing-lists/
This article might give you a solution:
http://www.linuxjournal.com/content/convert-spreadsheets-csv-files-python-and-pyuno-part-1v2
What version of LibreOffice are you using? (I haven't tested
command-line export of xls for a while)
Thanks,
--R