Signed the offer letter. Want to revert back.

Hi,
I am a software engineer with 4+ years experience, residing in Pune, India. I recently had an offer from Malaysian company and I accepted it by signing the Offer letter and gave a go ahead for EP process.
But now I am unable to join due to family concerns. I want to mail the HR of new employer and inform them about it.
Will my name be blacklisted as EP is in middle of the process?
Since I have signed the offer letter will they ask me to pay any amount?
Please help!

Additional information:
I signed the offer letter last week of july and expected to  report to work last week of august. Employer told me that he will initiate EP process and he shall update me after it is done. I had sent him copies of my passport along with other documents.

vid_158,
My 2 cents: Inform the HR that you wish to rescind the job offer ASAP. If you delay any further, they may have already made the arrangement to apply for your EP.

Yes, act as quickly as possible. Give a clear reason (it better be good!!). You may run into problems, it depends. Just ring them immediately and confirm by email. Be on your very best charm offensive mode.