Saudi Arabia says two of its oil tankers were among those targeted in a "sabotage attack" off the coast of the United Arab Emirates.
The UAE issued a statement on Sunday (May 12) saying that four commercial vessels had been hit, without giving any details of what had actually happened.
It confirmed there had been no casualties or spills.
The incidents occurred near Fujairah port - one of the world's largest bunkering hubs.
It lies just outside the Strait of Hormuz, which separates the Gulf states from Iran.
The strait is a major global oil and gas shipping route and, lately, has been in the media spotlight as tensions between Iran and the United States escalate.
Washington says it's received threats from Iran and has sent an aircraft carrier - and other forces - to the region.
Iran is under pressure after the U.S. tightened sanctions this month, getting rid of waivers that had allowed some countries to buy its oil.
Tehran responded by declaring that it will not allow its oil exports to be halted.
Following news of the attacks, Iran's foreign ministry called for an investigation into what it called "worrisome and dreadful" incidents.