Saudi Arabia says two of its oil tankers were sabotaged off the coast of the United Arab Emirates (UAE) in attacks that caused "significant damage" to the vessels.
One of the ships was en route to pick up Saudi oil to take to the United States, Saudi Energy Minister Khalid al-Falih said on Monday.
The announcement by al-Falih came as the UAE's regional allies condemned the reported sabotage on Sunday of four ships off the coast of the port city of Fujairah.
On Sunday, Iranian and Lebanese media outlets aired reports of explosions at the city's port but UAE authorities said the reports were inaccurate.
Emirati officials have declined to elaborate on the nature of the sabotage to the ships or say who might have been responsible.
The reports come as the US warned ships that "Iran or its proxies" could be targeting maritime traffic in the region, and as the US is deploying an aircraft carrier and B-52 bombers to the Gulf to counter what it called "threats from Tehran".
Shortly after the Saudi announcement, Iran's Foreign Ministry called for further clarification about what exactly happened with the Saudi tankers.
The ministry spokesman, Abbas Mousavi, was quoted by the official IRNA news agency as saying there should be more information about the incident.
Mousavi also warned against any "conspiracy orchestrated by ill-wishers" and "adventurism by foreigners" to undermine the maritime region's stability and security.
Tensions have risen in the year since President Donald Trump withdrew the US from the 2015 nuclear deal between Iran and world powers, restoring US sanctions that have pushed Iran's economy into crisis.
Last week, Iran warned it would begin enriching uranium at higher levels in 60 days if world powers failed to negotiate new terms for the deal.
In his statement, al-Falih said the attacks on the two tankers happened at 6am on Sunday.
"One of the two vessels was on its way to be loaded with Saudi crude oil from the port of Ras Tanura, to be delivered to Saudi Aramco's customers in the United States," al-Falih said.
"Fortunately, the attack didn't lead to any casualties or oil spill; however, it caused significant damage to the structures of the two vessels."
Saudi Arabia did not identify the vessels involved, nor did it say whom it suspected of carrying out the alleged sabotage.
Underlining the regional risk, the general-secretary of the six-nation Gulf Cooperation Council described the alleged sabotage as a "serious escalation" in an overnight statement.
"Such irresponsible acts will increase tension and conflicts in the region and expose its peoples to great danger," Abdullatif bin Rashid al-Zayani said.
Bahrain, Egypt and Yemen's internationally recognised government similarly condemned the alleged sabotage.
A statement on Sunday from the UAE's Foreign Ministry put the ships near the country's territorial waters in the Gulf of Oman, east of the port of Fujairah.
It said it was investigating "in cooperation with local and international bodies."
Earlier on Sunday, Lebanon's pro-Iran satellite channel Al-Mayadeen, quoting "Gulf sources", reported that a series of explosions had struck Fujairah's port.
State and semi-official media in Iran picked up the report from Al-Mayadeen, which later published the names of vessels it claimed were involved.
AP news agency, after speaking to Emirati officials and local witnesses, found the report about explosions at the port to be unsubstantiated.
Fujairah's port is about 140km south of the Strait of Hormuz, the narrow mouth of the Gulf through which a third of all oil at sea is traded.
The facility handles oil for bunkering and shipping, as well as general and bulk cargo.
It is seen as strategically located, serving shipping routes in the Gulf, Indian subcontinent and Africa.
Sunday's incident comes after the US Maritime Administration, a division of the US Transportation Department, warned on Thursday that Iran could target commercial sea traffic.
"Since early May, there is an increased possibility that Iran and/or its regional proxies could take action against US and partner interests, including oil production infrastructure, after recently threatening to close the Strait of Hormuz," the warning read.
"Iran or its proxies could respond by targeting commercial vessels, including oil tankers, or US military vessels in the Red Sea, Bab-el-Mandeb Strait or the Persian Gulf."
Early on Sunday, the agency issued a new warning to sailors about the alleged sabotage, while stressing "the incident has not been confirmed".
It urged shippers to exercise caution in the area for the next week.
It remains unclear if the previous warning from the US Maritime Administration is the same perceived threat that prompted the White House to order the USS Abraham Lincoln aircraft carrier strike group and B-52 bombers to the region on May 4.