Saudi Arabia said Monday two of its oil tankers were damaged in "sabotage attacks" in the Gulf as tensions soared in a region already shaken by a standoff between the United States and Iran.
It came as US Secretary of State Mike Pompeo scrapped a planned visit to Moscow to head to Brussels instead for talks with European officials on Iran.
Tehran called for an investigation into the "alarming" attacks and warned of "adventurism" by foreign players to disrupt maritime security.
The United States has already strengthened its military presence in the region, including deploying a number of strategic B-52 bombers in response to alleged Iranian threats.
Saudi Arabia, the Islamic republic's regional arch-rival, condemned "the acts of sabotage which targeted commercial and civilian vessels near the territorial waters of the United Arab Emirates," a foreign ministry source said.
"This criminal act constitutes a serious threat to the security and safety of maritime navigation and adversely impacts regional and international peace and security," the source added.
The UAE said on Sunday that four commercial vessels of various nationalities had been targeted by acts of sabotage off the emirate of Fujairah.
Saudi Energy Minister Khalid al-Falih said the two tankers suffered "significant damage" but there were no casualties or any oil spill.
"Two Saudi oil tankers were subjected to a sabotage attack in the exclusive economic zone of the United Arab Emirates, off the coast of the Emirate of Fujairah, while on their way to cross into the Arabian Gulf," the SPA state news agency quoted Falih as saying.
Fujairah port is the only terminal in the UAE located on the Arabian Sea coast, bypassing the Strait of Hormuz, through which most Gulf oil exports pass.
Iran has repeatedly threatened to close the strait in case of a military confrontation with the United States.
One of the two tankers that was attacked was on its way to be loaded with crude oil from a Saudi oil terminal for customers in the United States, Falih said.
- 'Serious development' -
The UAE did not accuse anyone of responsibility but warned that "carrying out acts of sabotage on commercial and civilian vessels and threatening the safety and lives of those on board is a serious development".
No one was hurt and Abu Dhabi called on world powers to help keep maritime traffic safe.
Iranian foreign ministry spokesman Abbas Mousavi expressed concern over the incident and its possible consequences.
"The incidents in the Sea of Oman are alarming and regrettable," Mousavi said in an English-language statement on the ministry's website.
He also "warned against plots by ill-wishers to disrupt regional security" and "called for the vigilance of regional states in the face of any adventurism by foreign elements", the statement added.
Almost all the oil exports of Saudi Arabia, Iraq, UAE, Kuwait, Qatar and Iran itself, at least 15 million barrels per day, are shipped through the Strait of Hormuz.
The Saudi minister denounced the attack on the vessels, saying it "aims to undermine the freedom of maritime navigation and the security of oil supplies to consumers all over the world."
He also urged the international community to "protect the safety of maritime navigation and the security of oil tankers, to mitigate against the adverse consequences of such incidents on energy markets, and the danger they pose to the global economy."
The UAE had earlier categorically denied reported on social media of massive explosions in oil tankers in the emirate.
The Pentagon said Friday that it was deploying an amphibious assault ship and a Patriot missile battery to the Middle East to bolster an aircraft carrier force sent to counter alleged Iranian threats.
The increasing tensions come after Tehran said Wednesday it had stopped respecting limits on its nuclear activities agreed under a 2015 deal with major powers.
Iran said it was responding to the sweeping unilateral sanctions that Washington has reimposed since it quit the agreement one year ago, which have dealt a severe blow to the Iranian economy.
Pompeo revised his travel plans to include a visit to Brussels on Monday to hold talks with French, British and German officials on "pressing matters" including Iran, a State Department official said
As a result, the top US diplomat is scrapping a stop expected on Monday in Moscow, but will still head to the Russian Black Sea resort of Sochi on Tuesday to meet President Vladimir Putin and Foreign Minister Sergei Lavrov.