DUBAI, April 2 (Reuters) - Stock markets in the Gulf moved sideways in thin volumes early on Sunday, while shares of the newly formed lender in Abu Dhabi, First Abu Dhabi Bank, outperformed a day after the legal completion of the merger.

Dubai's index was down 0.2 percent in thin trade with the majority of trade focused on second the third tier stocks. GFH Financial Group GFH.DU was down 1.2 percent.

But number of advancing shares outnumbered declining ones 14 to 11. Islamic Arab Insurance was up 3.6 percent.

In Abu Dhabi, the index was up 0.4 percent, buoyed by a 4.4 percent jump in shares of oil explorer and power supplier Abu Dhabi National Energy . Shares of the company are still down 7.6 percent since the start of the year.

On Thursday TAQA had reported a full-year loss of 18.55 billion dirhams ($5.05 billion) for 2016. The net loss was largely fuelled by a 16.9 billion dirham post-tax impairment and because of lower oil prices.

Shares of First Abu Dhabi Bank - the new name of the newly merged National Bank of Abu Dhabi and First Gulf Bank - were up 2.0 percent in their first 90 minutes of trade as a new entity. Shares of First Gulf Bank have been delisted.

In Saudi Arabia, the share index was up 0.2 percent in the first 45 minutes of trade as most petrochemical producers rose. Petro Rabigh was up 1.2 percent.

Saudi Industrial Investment Group , however, was down 1.0 after the company said its Saudi Chevron Phillips project would undergo 35 days of maintenance from April 1. The financial impact will be reflected in the second quarter results.

Shares of Saudi real-estate developer Jabal Omar rose 1.5 percent after the company said that one of its Mecca hotels started operations.

(Reporting by Celine Aswad; Editing by Saeed Azhar) ((celine.aswad@thomsonreuters.com)(+9715 62247653)(Reuters Messaging: celine.aswad.thomsonreuters.com@reuters.net))