Iran's government dismissed Sunday the United States' claim that Tehran is behind the attacks on Saudi oil facilities, and as warmongering rhetoric escalates fears of an all-out Iran-U.S. conflict reignite in the region.

"Iran has now launched an unprecedented attack on the world's energy supply," U.S. Secretary of State Mike Pompeo tweeted Sunday, adding that “there is no evidence the attacks came from Yemen.”

The accusation, in which no proof was presented, was rejected by Iran’s Minister of Foreign Affairs Javad Zarif, who responded by saying Washington shifted from a failed campaign of “maximum pressure” to one of “maximum lying” and “deceit,” adding that Yemen’s situation won’t be solved by blaming Iran.

Iranian Foreign Affairs Ministry spokesman Abbas Mousavi also criticized Saudi Arabia for fueling the flames of war in the region by committing various war crimes in Yemen and hailed the country for putting up resistance in the face of the aggression.

As tensions increase, President Donald Trump warned that the U.S. believes it “knows” who was behind the attacks on the Saudi oil facilities and is “locked and loaded,” but waiting for verification and for a Saudi assessment of responsibility before deciding how to proceed.

While Iran's Revolutionary Guard Corps issued a statement warning that although neither country wants a military conflict if it comes down to it, Iran is prepared for a "full-scale war". The commander of the IRGC aerospace arm Brigadier-General Amir Ali Hajizadeh noted Iran's missiles could hit U.S. bases and ships within a range of 2,000 km.

All this comes as Yemen’s Houthi forces Saturday attacked the state-run oil company Aramco’s Abqaiq plant, the world’s biggest petroleum processing facility, in a strike that cut more than half the Kingdom’s output or more than five percent of global oil supply.

A Saudi source told Reuters the damages inflicted on the oil facilities in the recent drone attacks are so massive that it is not clear when the country's oil output can return to normal.

As the world faces a possible production shortage of as much 150 million barrels per month, Trump authorized on Sunday the release of oil from the U.S. Strategic Petroleum Reserve (SPR) if needed in a quantity to be determined. While oil prices surged more than 15 percent to their highest level in nearly four months at the open on Sunday.

Dubbed as the “Forgotten War,” the Yemeni civil war started on March 26, 2015, when Saudi Arabia and the United Arab Emirates led a coalition of countries in a military campaign against the Houthis in Yemen in support of the Saudi-backed government of Abd-Rabu Mansour Hadi.

The conflict has since turned into a proxy war between Saudi Arabia, the UAE, and Iran. A narrative rejected by the Houthis who say that they took power from the Saudi-backed government in order to end Saudi interference into the country's affairs.