Iran 'almost certainly' behind ship attacks off UAE: Bolton

US National Security Advisor John Bolton said Wednesday that Iran was almost certainly behind oil tanker attacks that sent Gulf tensions soaring -- an accusation Tehran dismissed as "laughable".

The new war of words came on the eve of emergency Arab and Gulf summits called by Iran's regional rival Saudi Arabia to discuss the standoff and ways to isolate Tehran.

It follows a US military buildup that includes the deployment of an aircraft carrier, B-52 bombers and 1,500 more troops to the region.

Speaker during a visit to the UAE capital Abu Dhabi, Bolton said that additional US forces were sent to the Middle East as a "deterrent" and that Washington's response will be prudent.

The four ships, including two Saudi tankers, sabotaged off the Emirati coast on May 12 were attacked using "naval mines almost certainly from Iran", Bolton told a press conference.

"There's no doubt in anybody's mind in Washington who's responsible for this," he said in a clear reference to Iran.

Bolton however declined to provide specific evidence for Iran's hand in the attacks.

"Not going to get into the specifics. That's something the ship owners and the countries involved will release at their discretion. But I think it's important for the leadership in Iran to know that we know," he said.

- 'EVIL DESIRES FOR CHAOS' -
Iran strongly rejected the accusation.

"Making such laughable claims... is not strange" coming from the US, foreign ministry spokesman Abbas Mousavi said.

"Mr Bolton and other warmongers and chaos seekers should know that the strategic patience, high vigilance and complete defensive readiness of the Islamic Republic of Iran... will prevent the fulfilment of their evil desires for chaos in the region," Mousavi added.

US experts are part of a five-nation team that is investigating the attacks off the UAE emirate of Fujairah.

Two days after they took place Yemen's Huthi rebels -- accused by Abu Dhabi and Riyadh of being proxies of Tehran -- hit a strategic diversionary pipeline in Saudi Arabia with two drones.

The east-west pipeline, which has the capacity to carry some five million barrels per day from the oilfields of the kingdom's Gulf coast to the Red Sea, was shut for two days as a result of the attack.

Bolton said that there has also been "an unsuccessful attack on the Saudi port of Yanbu a couple of days before the attack on tankers."

Yanbu is Saudi Arabia's largest oil terminal on the Red Sea and is home to oil refineries and export facilities.

- 'TRYING TO BE PRUDENT' -
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 are responding and consulting more closely with our allies in the region to discuss what to do next," he said.

"We are trying to be prudent and responsible. We gathered evidence about the nature of attacks on the tankers and the east-west pipeline, and sent additional forces to act as a deterrent."

Bolton was due to leave the UAE later Wednesday for London as part of preparations for a visit there by US President Donald Trump.

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.

Regional tensions have spiked since Trump's administration reimposed sanctions against Iran after Washington unilaterally pulled out of a multilateral 2015 nuclear accord signed with the Islamic republic.

The Trump administration has ordered non-essential diplomatic staff out of Iraq, citing threats from Iranian-backed Iraqi armed groups.

But Trump appeared to soften his hawkish tone towards Tehran, saying during a visit to Japan on Monday that his government does not seek "regime change".

Bolton said Washington wants to prevent the Islamic republic from producing nuclear weapons, downplaying differences in the US administration on the issue.

"There's no mistake here. That we all have the same objective of keeping Iran from getting deliverable nuclear weapons."