May 9 (Reuters) - Al Rajhi Bank, world's largest Islamic bank by assets and market capitalisation, has started selling 5.5-year Islamic bonds, or sukuk, a document seen by Reuters showed on Thursday.

The initial price guidance for the perpetual non-callable debt has been placed at around 6.875%, the document said.

The deal is reported to be benchmark in size, typically understood to be at least $500 million, which will be issued under the bank's $5 billion Additional Tier 1 Capital Certificate Issuance Programme, the document added.

(Reporting by Shamsuddin Mohd; editing by Jason Neely)

((Shamsuddin.Mohd@thomsonreuters.com;))