Can I break signed job offer?

Show the job offer letter to local counsel to advise if there are any penalties or liabilities that can affect you if you break the deal.

You can always welch on a deal--but there may be consequences for doing so, as attorney Wolf points out. But you also pointed out that you have not signed the contract yet, right? If you haven't signed anything yet (and I mean anything at all), then you should be free to walk away. If you have signed anything with them, then take that to an attorney and have them give it a quick look. It shouldn't cost a lot of money for a quick review like that and that little fee might save you some trouble if/when you do decide to cut and run.

Counsels give good advice. A lawyer must look at the language in whatever you signed. MUCH better to pay an attorney's fee now before things get ugly.