*Attack halts 5.7mn barrels per day or about 6% of the world's oil supply

Saudi Arabia raced on Sunday to restart operations at oil plants hit by drone attacks which slashed its production by half, as Iran dismissed US claims it was behind the assault.

Houthi rebels in neighbouring Yemen, where a Saudi-led coalition is bogged down in a five-year war, have claimed Saturday's strikes on two plants owned by state giant Aramco.

But United States Secretary of State Mike Pompeo pointed the finger squarely at Tehran, saying there was no evidence the "unprecedented attack on the world's energy supply" was launched from Yemen.

"The United States will work with our partners and allies to ensure that energy markets remain well supplied and Iran is held accountable for its aggression," the top US diplomat added.

That drew an angry response from Tehran, where a foreign ministry spokesman said: "Such fruitless and blind accusations and remarks are incomprehensible and meaningless."

The remarks were designed to damage Iran's reputation and provide a pretext for "future actions" against the Islamic republic, he added.

Baghdad, caught between its two main sponsors -- Tehran and Washington -- also denied any link to the attacks amid media speculation that the drones were launched from Iraq.

Saudi de facto ruler Crown Prince Mohamed bin Salman, has said the kingdom is "willing and able" to respond to this "terrorist aggression".

Instead, the kingdom focused on restoring production at the plants, as the Saudi bourse slumped 3% as the week's trading began on Sunday morning.

Saturday's explosions set off fires that engulfed the Abqaiq plant, the world's largest oil processing facility, and nearby Khurais, which hosts a massive oil field.

Saudi's energy infrastructure has been hit by the Huthis many times before, but this strike was of a different order, abruptly halting 5.7 mn barrels per day (bpd) or about 6% of the world's oil supply.

The full extent of the damage was not clear, nor the type of weapons used.

Saudi interior ministry spokesman Mansour al-Turki said there were no casualties in the attacks.

Aramco has said it will dip into its reserves to offset the disruption, but the incident could affect investor confidence as its stock market debut looms. Aramco CEO Amin Nasser said Saturday that "work is underway" to restore full production.

And newly appointed Energy Minister Prince Abdulaziz bin Salman said part of the drop would be offset by drawing on vast storage facilities designed to be tapped in times of crisis.

Riyadh, the world's top crude exporter, has built five giant underground storage facilities across the country that can hold tens of millions of barrels of various refined petroleum products.

The US response to the attack throws into doubt reported efforts by Trump to arrange a meeting with Iranian President Hassan Rouhani at the upcoming United Nations assembly.

*****

Kuwait tightens security after drone sighted

Prime Minister Sheikh Jaber Mubarak al-Hamad al-Sabah has instructed the country's military and security leaders to tighten security around vital sites. Kuwait's Acting Interior Minister, Deputy Prime Minister and Minister of State for Cabinet Affairs Anas al-Saleh revealed that a probe has been launched after a drone was detected flying on the outskirts of Kuwait City, pointing out that proper security precautions will be taken in response. Page --

******

Attacks not launched from Yemen: US

The scope and precision of attacks on Saudi Arabian oil facilities suggest the launch was not made by Houthis and came from a west-northwest direction, not south from Yemen, a US official said on Sunday. "There's no doubt that Iran is responsible for this. No matter how you slice it, there's no escaping it. There's no other candidate. Evidence points in no other direction than that Iran was responsible for this," the official told Reuters. A foreign ministry spokesman in Tehran termed the accusations 'incomprehensible and meaningless'.

Related Story