JOIN USTehrik-e-Taliban Pakistan spokesman Ehsanullah Ehsan made the remarks in an interview with BBC Urdu.
Ehsan noted that Khan had said he is not a Taliban supporter and remarked: "We also think Imran Khan is not our sympathiser."
The Taliban spokesman advised Khan to talk in Urdu, the language of the Pakistani people, if he considers himself the representative of the people.
In a recent interview with the BBC, Imran had said that he is a liberal and does not support the militants.
But the Taliban spokesman said: "Those who call themselves as liberal are in fact free of Islam and other religions. A liberal man does not believe in any religion and particularly does not believe in Islam."
Ehsan questioned Khan's remarks describing several Pakistani leaders as slaves of the US.
He claimed Khan was a "slave of those Americans who are no more in the world".
Khan, who heads the Pakistan Tehrik-e-Insaf party, drew a mammoth crowd during a recent rally organised in Lahore as part of efforts to galvanise his supporters ahead of the general election scheduled for 2013.
He has called for the halting of military operations against groups like the Taliban and for dialogue to end the unrest in northwest Pakistan.