July 8 (Reuters) - Major Gulf stock markets fell on Wednesday as renewed fighting in the region and new U.S. sanctions on Iranian oil raised doubts about the sustainability of the ceasefire.

The United States said it bombed Iranian air defense systems, coastal surveillance facilities and drone launch sites, while Iran’s Revolutionary Guard said it targeted U.S. military sites in Bahrain and Kuwait, where air raid sirens sounded on Wednesday.

Washington also revoked the waiver that allowed Tehran to sell oil on the global market, a move the Iranian Foreign Ministry said violated the framework agreement aimed at ending the war.

A Qatari liquefied natural gas tanker was at risk of exploding, and a Saudi-flagged crude oil tanker sustained damage near the Strait of Hormuz on Tuesday, causing oil prices to rise. Maritime authorities raised the threat level for ships transiting the waterway to "severe."

Brent crude futures rose 3.2 percent to $76.56 a barrel by 0645 GMT.

The Saudi index fell 0.2 percent, with Al Rajhi Bank shares declining 0.3 percent. However, shares of oil giant Saudi Aramco rose 0.5 percent.

Dubai's index fell 1 percent, weighed down by a 1.2 percent drop in Emaar Properties shares and a 1.4 percent decline in Dubai Islamic Bank shares.

In Abu Dhabi, the index fell 0.7 percent, with shares of Alpha Abu Dhabi Holding dropping 1.6 percent.

The Qatari index fell 0.4 percent, with shares of Qatar National Bank, the largest bank in the Gulf, declining 0.4 percent.