June 25 (Reuters) - Major Gulf stock markets fell at the start of trading on Thursday, pressured by lower oil prices and growing expectations of a U.S. interest rate hike this year.

Oil prices, a key driver of Gulf markets, continued to fall, approaching levels seen before the outbreak of the Iran war, as expectations of increased supply from the Middle East outweighed concerns about demand.

The preliminary agreement reached last week aimed at ending the US-Israeli war on Iran, which began on February 28, has allowed for the resumption of shipping traffic through the Strait of Hormuz.

The main Saudi market index fell 0.3 percent, affected by a 0.5 percent drop in shares of the National Bank of Saudi Arabia, the country's largest bank by assets.

The main index of the Qatar Stock Exchange stabilized amid volatile trading.

The rising inflation rate in the United States, fueled by the war with Iran, and the Federal Reserve's (the US central bank) tendency to tighten monetary policy, have contributed to strengthening expectations of an interest rate hike.

According to the CME FedWatch tool, traders expect three US interest rate hikes this year, and estimate the probability of a September hike at approximately 67 percent.

Changes in US monetary policy have a significant impact on Gulf markets, as most of the region's currencies are pegged to the dollar.

Dubai's main stock market index fell 0.2 percent, weighed down by a 1.2 percent drop in Dubai Islamic Bank shares.

The main index in Abu Dhabi lost 0.3 percent.