how to include lxml in depenency list of python package with setuptools?

I have used the following code in setup.py file

setup(...,    install_requires=[       'lxml'      ],      .....)

But when i install the package it gives the following error

    Scanning index of all packages (this may take a while)Reading http://pypi.python.org/simple/No local packages or download links found for lxmlerror: Could not find suitable distribution for Requirement.parse('lxml')

How to make the setup to install lxml library ?

Thanks for the help :)