Mr Rakesh Srivastav,
It is very much a high sea sale. Whether the sales tax officer accepts or not it is exempt because it is again exported. A high sea sale of the type mentioned by you is not refered in the CST Act 56.There a high sea sale made to local dealer is given exemption.Here some points are to be noted :
1) When this high sea sale takes place before the goods reaching the custom barriers of India it becomes a sale exempt under section 3 itself, because ithe goods never enter or cross any state border at all.
2) To be called as a high sea sale the purchase from Sri lanka should be made for the purpose of meeting the order of the US customer.
3)However, as both import and export are exempt under all VAT Acts there should be no problem in this case.
MJK