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Donald Trump's national security adviser claimed Wednesday - without offering evidence - that the alleged sabotage of four oil tankers off the coast of the United Arab Emirates came from naval mines placed "almost certainly by Iran".

"There's no doubt in anybody's mind in Washington who's responsible for this," John Bolton told a press conference in the Emirati capital Abu Dhabi.

"Who else would you think is doing it? Someone from Nepal?"

US experts are part of a five-nation team that is investigating the May 12 attacks that damaged the four vessels in the Sea of Oman off the UAE emirate of Fujairah.

Bolton, long a hawk on Iran, also said there was "no reason" for Iran to back out of its nuclear deal with world powers other than to seek atomic weapons, a year after the US president unilaterally withdrew America from the accord.

Bolton further told journalists that there had been a previously unknown attempt to attack the Saudi oil port of Yanbu as well. Yanbu is the end point of the kingdom's East-West Pipeline which was attacked in recent days in a coordinated drone assault launched by Yemen's Houthi rebels.

Bolton said he would meet Abu Dhabi Crown Prince Sheikh Mohammed bin Zayed Al-Nahyan as well as his UAE counterpart, Sheikh Tahnoun bin Zayed Al-Nahyan, to discuss relations and regional tensions.

"We remain concerned and as watchful as we can," he said. "We are responding and consulting more closely with our allies in the region to discuss what to do next."

In recent weeks, tensions have soared as the US beefed up its military presence in the Persian Gulf in response to a still-unexplained threat from Iran.

The US has accused Iran of being behind a string of incidents, including the alleged sabotage of oil tankers near the UAE coast and a rocket that landed near the US Embassy in Baghdad, while Yemen's Iranian-aligned Houthi rebels have launched a string of drone attacks targeting Saudi Arabia.

Tehran called the attacks on the ships "alarming and regrettable", and warned of "adventurism" by foreign players to disrupt maritime security.

Fujairah, where the attacks took place, is a key oil export terminal on the Sea of Oman that spares tankers the need to enter the Gulf through the strategic Strait of Hormuz, which Iran has repeatedly threatened to close.

Almost a third of the world's oil supplies pass through the narrow strait between Iran and Oman which is the sole shipping lane into and out of the Gulf.

Meanwhile, Iran has announced it is backing away from the landmark 2015 nuclear deal which saw it limits its enrichment of uranium in exchange for the lifting of economic sanctions. Trump withdrew the US from the accord as he believes it didn't go far enough.

Bolton said that without more nuclear power plants, it made no sense for Iran to stockpile more low-enriched uranium as it now plans to do. But the US also earlier cut off Iran's ability to sell its uranium to Russia in exchange for unprocessed yellow-cake uranium.

Iran long has insisted its nuclear program is only for peaceful purposes. However, Western powers pushed for the nuclear deal to limit Iran's ability to seek atomic weapons.

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