DUBAI — The United Arab Emirates said today that a Japanese oil tanker was hit by an explosives-laden dinghy in the Persian Gulf in what would be the first terror attack in the strategic waterway.

The report — which came days after an al-Qaida-linked group claimed responsibility for attacking the vessel — raised fears about the vulnerability of the Strait of Hormuz, a vital shipping lane for many petroleum exporting countries.

It was the latest in what has been a series of conflicting accounts of what happened to the M. Star supertanker, which was damaged as it entered the Strait of Hormuz, a transit point for about 40 percent of oil shipped by tankers worldwide.

Al-Qaida has carried out attacks on oil infrastructure on land in nearby Saudi Arabia, as well as a 2002 suicide bombing of the Limburg off the coast of Yemen and the 2000 bombing of the USS Cole in the Yemeni port of Aden.

But if the UAE report is confirmed, the July 28 incident would be the first militant attack in the strait, a narrow chokepoint between Oman and Iran. For years, fears have been high that the waterway could be the site of conflict between the United States and Iran, but the reported attack underscored concerns that militant groups could target civilian vessels to foment economic instability.