By Hadeel Al Sayegh and Tom Arnold

DUBAI, Dec 28 (Reuters) - Four top managers at National Bank of Abu Dhabi NBAD.AD (NBAD) are leaving the bank ahead of a merger with First Gulf Bank FGB.AD (FGB) to create one of the Middle East and Africa's biggest banks, according to sources.

Abdulla Mohammed Saleh AbdulRaheem, deputy group chief executive and Qamber al-Mulla, senior managing director and chief executive of Gulf and international, are both departing, the sources said.

Also leaving are Saif al-Shehhi, senior managing director UAE government group and VVIP clients, and Abdulla Bin Khalaf al-Otaiba, senior managing director and group head of global retail & commercial.

NBAD was not immediately available to comment.

NBAD and FGB won shareholder approval earlier this month for a merger to create a banking heavyweight with $175 billion in assets.

The tie-up, expected to be completed during the first quarter, is part of a move by Abu Dhabi to revamp its economy after more than two years of lower oil prices weighing on state revenues.

The merger is expected to lead to some reduction in staffing across the two banks, but it was unclear whether the departure of the four senior management was linked to any redundancies.

The two banks said in October that they had finished picking the senior management team to run the combined bank.

FGB board member and managing director Abdulhamid M. Saeed had already been tapped to lead the new bank, with NBAD chief financial officer James Burdett assuming the same role at the merged entity.

The remaining appointments will be announced ahead of the completion of the merger, a statement from FGB at the time said.

NBAD's chief executive at the time of the merger deal, Alex Thursby, left his role in August, with Abhijit Choudhury becoming acting chief executive.











(Editing by Louise Heavens) ((Tom.Arnold@thomsonreuters.com; +97144536265; Reuters Messaging: tom.arnold.thomsonreuters.com@reuters.net))