The September attack on Saudi Aramco's facilities that temporarily shut down half of the kingdom's oil production represented an act of war by the Iranian state, U.S. special representative for Iran Brian Hook told CNBC on Saturday.
"Because of the Iran nuclear deal we've been accumulating risk of a regional conflict — and what Iran did to Saudi Arabia on September 14 was an act of war," Hook told CNBC's Hadley Gamble during the Doha forum in Qatar.
Iran's government has stringently denied involvement in the drone and missile attack, considered to be the most significant assault on oil infrastructure in history.
Riyadh, alongside Washington and several other Western allies, has accused Iran of involvement in the attack. But it has not directly accused the Islamic Republic of carrying out an act of war — something seen as an attempt to avoid greater escalation.
"To launch an attack from your territory, if that is the case ... this would be considered an act of war," Saudi Minister of State for Foreign Affairs Adel al-Jubeir said in late September. But the kingdom maintains it is currently seeking a peaceful resolution.
In response to the suggestion that nothing has been done to Iran as a result of its suspected attack, Hook emphasized the role of diplomacy and the United Nations — something that the Donald Trump administration has been accused of ignoring.
"We have, but Iran is more diplomatically isolated as a consequence of it," Hook said. "We still see a role for the UN Security Council to play, and now that Saudi has concluded its investigation, we hope they will do (something) with the UN Security Council."
The Trump administration has sent some 14,000 additional U.S. troops to the Gulf region since last spring and has pledged to continue supporting and enhancing Saudi Arabia's air defenses.
The Trump administration's "maximum pressure" campaign of heavy sanctions and economic isolation has brought the Iranian economy to its knees, with a 9% economic contraction expected by the International Monetary Fund, a currency in free fall, more than 40% inflation and recent protests across the country in response to austerity measures and spikes in the price of fuel and other basic goods.
It's also hit the coffers of Lebanese political and militant group Hezbollah, which gets 70% of its funding from Iran.
But the measures, which Tehran calls "economic terrorism," have so far failed to deter the kind of destabilizing behavior that the U.S. accuses Iran of carrying out in the region — whether it's backing Houthi rebels in Yemen, funding Hezbollah, Shiite paramilitary groups in Iraq, or the accused Aramco attacks.
"As to whether they're going do it again, modern terrorism has an asymmetric advantage over conventional deterrence," Hook said in reference to the September 14 strikes. "We know that because we have enhanced our force posture in the region, we've deterred and disrupted a lot of attacks. But the asymmetric advantage that any terrorist regime enjoys, it's impossible to eliminate."
"So we hope that we've put in place the sort of deterrence that will avoid another attack, we've enhanced Saudi's air defenses and so have other countries, and we're going to continue to enhance Saudi defenses and our defenses in the region to avoid it from happening again."
In May, the Trump administration defied Congressional objections to complete a sale of more than $8 billion worth of weapons to Saudi Arabia, the United Arab Emirates and Jordan, citing rising tensions with Iran.