National Commercial Bank (NCB), Saudi Arabia's largest lender, is selling SR2 billion ($533 million) of capital-boosting sukuk, two banking sources with knowledge of the matter said on Sunday. The offer, which enhances the bank's Tier 1 - or core - capital and is compliant with Basel III banking regulations, is the third such transaction by NCB since June, and is part of a plan to raise as much as 7 billion riyals of capital before the end of 2015, one of the sources said. NCB didn't immediately respond to a request for comment.