Major stock markets in the Gulf moved sideways on Wednesday, with the Saudi index edging up ahead of a meeting on the future level of oil output cuts by the Organization of the Petroleum Exporting Countries (OPEC) and its allies.

Key members of OPEC and allies including Russia, collectively known as OPEC+, are set to decide whether to extend output cuts of 9.7 million barrels per day (bpd) that end in July or ease them to 7.7 million bpd.

The benchmark stock index in Saudi Arabia, the de facto leader of OPEC, added 0.3%. Al Rajhi Bank rose 0.5%, while National Commercial Bank was up 0.7%.

In Qatar, the index gained 0.5%, buoyed by a 1.3% rise in petrochemical firm Industries Qatar and 1% increase in Qatar Islamic Bank.

On Tuesday, the U.N.'s highest court for disputes between countries sided with Qatar in its legal fight with several Gulf states that imposed an air blockade against Doha. 

Saudi Arabia, the United Arab Emirates, Bahrain and Egypt severed political, trade and transport ties with Qatar in June 2017, accusing Qatar of backing Islamist radicals and Iran. Doha denied the charges and said the embargo aimed to undermine its sovereignty.

Dubai's main share index eased 0.2%, with the country's largest sharia-compliant lender Dubai Islamic Bank falling 0.5% and Commercial Bank of Dubai sliding 4.8%.

The Abu Dhabi index lost 0.3%, hurt by a 0.5% decrease in telecoms firm Etisalat and a 1.7% fall in Aldar Properties.

(Reporting by Ateeq Shariff in Bengaluru; Editing by Christopher Cushing) ((AteeqUr.Shariff@thomsonreuters.com; +918061822788;))