To give a brief history, I am Indian citizen and I worked for a technology start-up in India, it was a US based company which had its branch office in Hyderabad, India. Company was not public and I had purchased shares in employee stock options. Now this company is getting sold to another US based company and they are paying off all the shareholders. My question is : what is the tax implication in US? what form do I need to fill? Is the tax applicable for full capital gain? Since I need to pay taxes ( 30% ) in India, is there any way I can minimize my tax in US?

Thanks in advance.