If i buy an iPhone in US and use it in India will there be any issues in service and warranty?

Whether you get service is at the discretion of the people at the shop. They're not obligated to honor international iPhone warranties and may not be able to replace the unit with one that's functionally identical to the original.

(223587)

All it takes is a quick search hear to see that you will not be able to get it serviced in India at all.

if you intend to use it in India, buy a phone in India from an authorized retailer there.