DUBAI/LONDON (REUTERS, AFP) - Saudi Arabia said on Monday (May 13) that two Saudi oil tankers were among vessels targeted by a "sabotage attack" off the coast of the United Arab Emirates, condemning it as an attempt to undermine the security of global crude supplies.

On Sunday, the UAE foreign ministry said four commercial vessels were targeted by "sabotage operations" near the Fujairah emirate, one of the world's largest bunkering hubs lying just outside the Strait of Hormuz. It did not say who was behind the operation, which took place amid heightened tensions between the United States and Iran.

Iran's foreign ministry spokesman Abbas Mousavi called the incidents "worrisome and dreadful", and asked for an investigation into aspects of the matter.

Mr Mousavi was cited by the semi-official ISNA news agency as saying "such incidents have negative impact on maritime transportation security", and asking for regional countries to be "vigilant against destabilising plots of foreign agents".

The strait, a vital global oil and gas shipping route, separates the Gulf states and Iran, which has been embroiled in an escalating war of words with the United States over sanctions and the US military's presence in the region.

Oil prices rose on Monday, with Brent crude futures trading at US$70.98 a barrel in afternoon Asian trade.

Saudi Energy Minister Khalid al-Falih said in a statement that one of the two Saudi vessels attacked was on its way to be loaded with Saudi crude from Ras Tanura port for delivery to state-owned Saudi Aramco's customers in the United States.

The attack did not lead to any casualties or an oil spill but caused significant damage to the structures of the two vessels, said the statement, carried on state news agency SPA.

Trading and shipping sources identified the Saudi vessels as Bahri-owned very large crude carrier (VLCC) tanker Amjad and crude tanker Al Marzoqah. Bahri did not respond to a request for comment.

The UAE foreign ministry said on Sunday (May 12) there were no casualties and the Fujairah port operations were normal. An investigation had been launched in coordination with international authorities, and called on global powers to prevent any parties trying to harm maritime safety and security.

Saudi Arabia's foreign ministry in a separate statement voiced support for its close regional ally the UAE, the Middle East's trade and business hub.

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, and which Iran has repeatedly threatened to close in case of a military confrontation with the United States.

The small emirate has an oil terminal and a pipeline that delivers crude oil from Abu Dhabi which sits on the majority of UAE oil reserves.

The incident comes as the United States has strengthened its military presence in the region, including deploying a number of strategic B-52 bombers in response to alleged threats from Teheran.

It also comes as US Secretary of State Mike Pompeo is headed to Brussels to discuss Iran with French, British and German officials.

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 threats from Iran. Tehran has called the US military presence "a target" rather than a threat.

Teheran said last Wednesday (May 8) 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 re-imposed since it quit the agreement one year ago, which have dealt a severe blow to the Iranian economy.

Earlier this month, the Maritime Administration said US commercial ships including oil tankers sailing through Middle East waterways could be targeted by Iran in one of the threats to US interests posed by Teheran.

Washington tightened sanctions on Iran this month, eliminating waivers that had allowed some countries to buy its oil, saying it wanted to cut Teheran's crude exports to zero. Iran has said it will not let its oil exports by halted.