DUBAI - Gulf stocks opened in negative territory on Tuesday on the back of sliding oil prices and mirroring a slump in Asian stocks.

Brent futures reached a three-month low, trading at $71.67 per barrel by 0915 GMT, as Libyan ports reopened and traders eyed potential supply increases by Russia and other producers.

The Saudi index shed 0.2 percent in the first hour of trading, with petrochemical companies such as Saudi Kayan Petrochemical Co down 1.2 percent and heavyweight Saudi Basic Industries Corporation (SABIC) dropping 1.1 percent.

Banking stocks were also down. Riyad Bank, Saudi Arabia's fourth-largest lender by assets, shed 0.3 percent despite reporting earlier a 25.2 percent rise in second-quarter net profit, in line with analysts' forecasts.

The bank made 1.06 billion riyals ($282.64 million) in the three months to June 30, up from 848 million a year earlier, it said in a bourse filing. Three analysts polled by Reuters forecast a profit of 1.03 billion riyals. Deposits dipped 2.3 percent to 153.4 billion riyals.

In Dubai, where the index was down 0.1 percent, Drake and Scull International (DSI) jumped 4.5 percent after it said on Monday that Tabarak Investment, which has a 13.3 percent stake in the company, will continue to be a strategic investor.

DSI has been lagging because of concerns about its financial position, business outlook and the outcome of an investigation by United Arab Emirates authorities into financial violations by previous management.

Blue-chip Emaar Properties was down 0.4 percent after it said in a statement that it is exploring various financing options to streamline its business. It said so in response to a Financial Times article, which said the Dubai developer has put $1.4 billion in assets on sale amid a slump in the real estate market.

In Bahrain, Ahli United Bank jumped 6 percent after Kuwait Finance House (KFH) KFH.KW , the country's largest Islamic lender, announced on Monday that it had invited the Bahraini bank to begin a due diligence process for a potential merger. KFH was down 0.8 percent.

If a merger proceeds, the total assets of the two banks would be $90.57 billion, making it the sixth-largest bank in the Gulf on that measure, according to Thomson Reuters data.

($1 = 3.7503 riyals)

(Reporting by Davide Barbuscia, editing by Louise Heavens) ((Davide.Barbuscia@thomsonreuters.com; +971522604297; Reuters Messaging: davide.barbuscia.reuters.com@reuters.net))