Saudi National Bank, the kingdom's biggest lender, has launched a $850 million five-year Islamic bond, or sukuk, according to a bank document seen by Reuters on Tuesday.

The spread for the debt sale was set at 90 basis points over U.S. Treasuries, tighter than the initial guidance of 120 bps over the same benchmark earlier in the day. (Reporting by Shamsuddin Mohd; Editing by Kevin Liffey)