DUBAI, May 30 (Reuters) - First Abu Dhabi Bank is expected to raise $500 million from an offering of five-year green bonds, a bank document showed on Tuesday.

Guidance was tightened 20 basis points (bps) to around 100 bps over U.S. Treasuries after demand topped $1.4 billion, the bank document showed.

FAB, the UAE's biggest lender, is green structuring agent and is joined by Citi, Credit Agricole, HSBC and Standard Chartered as joint lead managers and bookrunners.

FAB last sold green bonds in October in a $700 million deal. It has also raised $1.6 billion through three public debt sales this year, including two sales of Islamic bonds known as sukuk and a sale of conventional bonds.

(Reporting by Yousef Saba; Editing by Kirsten Donovan)