National Commercial Bank (NCB), Saudi Arabia's largest lender, is selling a 2 billion riyal ($533.3 million) sukuk as part of its plans to raise capital, two banking sources with knowledge of the matter said.

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.

In the same way as the previous two issues, the latest sukuk is structured with a perpetual tenor but with a clause in the documentation which allows the bank to redeem the Islamic bond after a certain date, the two sources said, adding that NCB Capital was acting as sole arranger.

The transaction will be privately placed with one or more government-owned investment funds, the second source added.

NCB didn't immediately respond to a request for comment.

The bank's Tier 1 capital ratio had slipped to 14.2 percent at the end of June, down from 15.5 percent at the same point of 2014, according to its latest financial statement.

This figure would include the uplift from the 1 billion riyal sukuk sold in June, but not the 2 billion riyal trade which the bank announced on July 15 it had completed.