Saudi displayed arms that they believed were used in the Aramco attack.

Saudi Arabia's newly appointed energy minister was in London when he learned in the middle of the night of the largest-ever attack on the kingdom's oil infrastructure.

Prince Abdulaziz bin Salman, a veteran oil official and senior member of the Al Saud ruling family, hurried back to the kingdom, flying by private jet to Aramco's headquarters in Dhahran to assess the damage and manage the fallout from the attack on the world's largest oil exporter, three sources close to the matter said. Officials at state-run oil company Saudi Aramco, meanwhile, gathered in what was referred to internally as the "emergency management room" at the company's headquarters.

Interviews with at least a dozen Gulf and Western officials provide the most detailed account to date of the response by Saudi officials and state oil company Aramco to the most destructive strike on Saudi Arabia since it opened an offensive in Yemen more than four years ago. The attack knocked out more than half the kingdom's oil production, or almost 6 percent of global oil output.

Saudi Arabia has said Iran was responsible, an assessment that U.S. officials share.

Iranian officials were unavailable to comment but Iran has denied involvement.

Yemen's Houthi movement, an ally of Iran battling a Western-backed, Saudi-led coalition has claimed responsibility. But Gulf diplomats and regional officials say they are skeptical of the claim given the sophistication of the attacks.

The Saudi energy ministry declined to comment on its response to the attacks. The government communications office did not immediately respond to a request for comment.

The attacks place pressure on both U.S. President Donald Trump and Saudi Arabia's day-to-day leader Crown Prince Mohammed bin Salman, who have worked closely together to contain Iran's growing regional influence. Both nations have stressed the need for caution.

U.S. Secretary of State Mike Pompeo has described the attacks as "an act of war" against Saudi Arabia, though Trump says there are options short of war. Iran has warned that any U.S. or Saudi military strike against the country would bring "all-out war."

MISSILES AND DRONES

Shortly after 3:30 a.m. local time on Saturday, 25 drones and low-flying missiles struck two of Saudi Arabia's largest oil facilities located in the east of the kingdom, according to Saudi officials.

Amin Nasser, the chief executive of state-run Saudi Aramco, which owns the two plants, rushed to Aramco's emergency-response room at the company's headquarters in the oil-producing Eastern Province, where he was joined by other senior managers, according to several people briefed on the matter. There was a sense of shock at the scale of the damage, some of the people said.

By the time Aramco's team was dealing with the fires at the first site in Khurais, where more than 200 people were at the time, strikes were still hitting the facility, according to the company. More than a hundred contractors were immediately evacuated.

A Saudi Aramco spokesman declined to comment on questions from Reuters about the company and the CEO's response to the attacks.

Saudi officials believed Iran was responsible because the intensity of the attack was beyond the capability of the Houthi, but they wanted to gather evidence before going public with the claims, according to Gulf diplomats and regional officials.

Saudi officials also spoke to their allies, in some instances requesting assistance with experts to help with the investigation and help in strengthening air defenses. On Saturday, Prince Mohammed provided Trump an update by phone, according to a U.S. official. Trump offered "his support for Saudi Arabia's self-defense," according to the White House readout of the call.

U.S. officials also quickly came to believe that the attack did not come from Yemen and that Iran was responsible, according to U.S. officials who briefed reporters. The Houthi had not struck that distance before or in such a "precise and coordinated fashion," said a senior administration official.

"PHOENIX FROM THE ASHES"

By midday Saturday in Saudi Arabia, Nasser and other senior company Aramco executives were headed to the damaged plants, first to Khurais and then to Abqaiq, one of the sources briefed on the matter said.

That night, Nasser was joined at Abqaiq, the world's biggest oil processing facility, by Prince Abdulaziz and Aramco's new chairman Yassir al-Rumayyan, according to sources and pictures released by the state news agency.

Aramco, which runs a variety of large projects in the kingdom, deployed more than 5,000 contractors and pulled employees from other projects to work around the clock to bring production back, according to Nasser's public comments and one of the sources briefed on the matter.

Initial assessments were that the damage was significant and that bringing full production back online could take weeks or even months, said Saudi officials and industry sources who visited the sites or were briefed on the attacks.

Saudi oil officials were scrambling to produce a report on the extent damage for the kingdom's top leadership, including King Salman, the energy minister's father, according two of the sources briefed on the matter. But engineers needed 48 more hours for a final assessment, the people said.

Crude markets would begin trading again in two days and Saudi Arabia was under pressure to reassure buyers that oil supplies will not be disrupted.

"Imagine if this (production) didn't come back on time the whole global security of supply is going to be impacted," Nasser told reporters earlier this week. "We have a lot of projects in the kingdom... so we have all of the workforce that's needed to rebuild, reconstruct and put it back," he said.

By Tuesday, the kingdom had managed to restore full supplies to customers by drawing oil from their massive oil inventories. The company also announced production would return sooner than expected - by the end of the month. Aramco had emerged "like a phoenix from the ashes," said Prince Abdulaziz in remarks to news media that night in Red Sea city of Jeddah.

The news restored some confidence, prompting a fall in oil prices that had jumped on Monday.

ATTACK EVIDENCE

The Saudis continued to analyze the attack debris. That included aerial weaponry that missed their targets and was recovered just to the north, according to U.S. officials.

The United States dispatched to Saudi Arabia forensic specialists to assist in the effort; France said it was also sending investigative experts.

On Wednesday, Saudi Arabian officials publicly accused Iran of involvement. At a news conference, a defense ministry official displayed drone and missile debris it said was undeniable evidence of Iranian aggression and identified the drones as Iranian Delta Wing unmanned aerial vehicles.

"The attack was launched from the north and unquestionably sponsored by Iran," said the official, Colonel Turki al-Malki.

U.S. officials fingered southwest Iran as the staging ground, an assessment based at least in part on still-classified imagery showing Iran appearing to prepare an aerial strike, according to two U.S. officials.

On Thursday, the United States was considering sending anti-missile batteries, drones and more fighter jets to Saudi Arabia, U.S. officials said.

"Frankly there's just not enough defense capability in the country, if you could be hit from multiple directions," one U.S. official told Reuters.

It is possible the attacks were launched from more than one location, a Western security source said. "The exact launch location is important as it determines the response and there does have to be a response," the person said.

On Friday, repair work to the oil plants was ongoing. At the Khurais facility, parts of the facility were visibly burnt and pipes melted. During a tour of the site organized by the company, Fahad Abdulkarim, general manager for Aramco's southern area oil operations, told reporters that the company is shipping equipment from the United States and Europe to help repair the damage.