ISTANBUL — The assault on oil facilities in Saudi Arabia this weekend has highlighted what analysts say is a rapidly evolving threat from Iranian-made weapons in the region, marking a potentially alarming shift toward precision strikes on critical infrastructure.

U.S. officials believe that both cruise missiles and drones were used in the assault and that part of the operation, which was claimed by Yemen’s Houthi rebels, was launched from Iranian territory, according to a U.S. official. Iran has denied involvement in the attack.

President Donald Trump on Monday stopped short of directly blaming Iran for the attack, allaying, at least for the moment, fears of a military conflict between the United States and Iran.

Trump’s remarks stand in stark contrast to Secretary of State Mike Pompeo’s comments Saturday, which left no question about the responsible party.

“Iran has now launched an unprecedented attack on the world’s energy supply,” Pompeo said.

Officials in Washington and Riyadh spent the day analyzing satellite photos and other intelligence that they said indicated that Iranian weapons were used in the assault on the Saudi Aramco facilities. But they presented no new information that would conclusively show Iran directed or launched the attack, which Saudi officials said led to a 50% reduction in oil production.

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The Trump administration believes that Yemen’s Houthis, who receive Iranian support, also contributed to the assault, according to a U.S. official. There were between 17 and 19 direct hits on Saudi oil facilities in Abqaiq and Khurais, some 500 miles from Yemen’s border, the U.S. official said.

Neither Trump nor Saudi leaders would say unequivocally that Iran was responsible.

“It’s looking that way,” Trump said in the Oval Office, during a meeting with Bahrain’s crown prince. “As soon as we find out definitively, we’ll let you know.”

Trump’s reluctance to assign blame appeared to reflect his long-standing desire to keep the United States out of wars, despite his tweet Sunday that the United States was “locked and loaded depending on verification.”

“I’m not looking to get into new conflict, but sometimes you have to,” Trump said Monday.

Asked what message he wanted to send to Iran, the president replied, “I think I’ll have a stronger message, or maybe no message at all, when we get the final results of what we’re looking at.

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“There’s no rush,” he added.

Trump didn’t rule out a military response but made clear that the Saudis would take the lead — and pay the bill.

“The fact is that the Saudis are going to have a lot of involvement in this if we decide to do something. They’ll be very much involved, and that includes payment,” Trump said.

Saudi officials affirmed that Iranian weapons were used in the attack but also stopped short of singling out Iran in statements that appeared to reflect fears across the Persian Gulf of a wider and more violent conflagration.

Col. Turki al-Malki, the spokesman for the Saudi-led coalition fighting in Yemen, said initial investigations into the strikes on the oil facilities had found that “these weapons are Iranian weapons.” He added that the attacks “did not originate in Yemeni territory as claimed by the Houthi militias.”

“The Yemeni people have a right to respond” to Saudi military aggression, Iranian President Hassan Rouhani said Monday, calling the attack “reciprocal” and “legitimate defense.”

Iran maintains advanced missile and drone programs as part of its national-defense strategy and has transferred some of those weapons and technology to allied forces in the region, including Houthi fighters in Yemen, U.S. officials and weapons experts say. Iran’s drone and missile arsenals allow it to deter adversaries and support regional proxies, who can strike on Iran’s behalf, analysts say.

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“ … It enables Iran to operate from range, keep its territory safe and strike at faraway targets,” said Behnam Ben Taleblu, a senior fellow at the Foundation for Defense of Democracies. “Drones, missiles and rockets all feature into Iran’s asymmetric security strategy and are relatively cheaper to produce.”

According to the Washington-based Brookings Institution, Iran has become a “significant exporter of missiles, missile production capability and missile technologies,” including a long-range, land-attack cruise missile experts say may have been used in Saturday’s assault.

Iran and Saudi Arabia are chief rivals in the region, and the Saudi leadership has been a key advocate of the Trump administration’s campaign of “maximum pressure” against Iran. The United States has imposed harsh sanctions on the Iranian economy in a bid to compel Tehran to negotiate constraints on its missile programs and support for regional proxy forces.

Saudi defense systems apparently failed to detect the cruise missiles and drones swarming over its borders, underscoring the kingdom’s vulnerability to asymmetric warfare.

“I’m just surprised that they got caught with their pants down,” a contractor working for the Pentagon on drone defenses said of the Saudi security services. He spoke on the condition of anonymity because he was not authorized to speak to the media.

“They should have seen this coming,” he said.

According to a United Nations expert panel on Yemen, Houthi fighters have, in the past, used what are known as “suicide” or “kamikaze” drones, some of which are similar to Iranian models. The Houthis have “retained access to the critical components, such as engines, guidance systems, from abroad that are necessary to assemble and deploy them,” the panel report said.

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A combined assault using both drones and cruise missiles could, in theory, “help with confusing and overwhelming defense systems,” said Justin Bronk, a research fellow at the London-based Royal United Services Institute, offering strategic advantage to the attacker.

According to Markus Mueller, an analyst at the German Fraunhofer Group for Defense and Security, radar systems are typically able to identify drones flying over vast stretches of land, especially on even surfaces and outside cities or mountains areas.

The challenge, said Mueller, whose research focuses on unmanned aerial vehicles, or drones, is to be able to respond to sightings and immediately protect sensitive infrastructure.

But analysts also pointed to the alleged use of cruise missiles in the assault, which experts say are low-flying and far more difficult to detect, as a more worrying development. The missiles can be precision guided and allow for more devastating strikes on specific targets.

Iran has reverse-engineered a former Soviet land-attack cruise missile, the Kh-55, and has also used Chinese anti-ship missile technology to bolster its own capabilities and those of its proxies, weapons analysts say. During the 2006 war in Lebanon, Iran-backed Hezbollah extremists targeted an Israeli vessel with what weapons experts say was likely a Chinese C-802 anti-ship missile provided by Iran.

In its 2018 Worldwide Threat Assessment, the Office of the Director of National Intelligence said that Houthi rebels attempted a cruise-missile attack on an unfinished nuclear reactor in Abu Dhabi, the capital of the United Arab Emirates.

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Henry Rome, an analyst at the New York-based political risk firm Eurasia Group, said that if Iran is responsible, its strategy is to “build leverage for eventual talks with Washington.”

Iran wants to “compel the Trump administration to put their foot on the brakes of sanctions and push other countries to stand up for them,” Rome said.

U.S. military investigators arrived at the attack sites in Saudi Arabia within the past day and are gathering intelligence to learn more about the weapons used, a U.S. official said Monday.

Pentagon officials have urged restraint in any response, arguing against a potentially costly conflict at a time when the Pentagon is seeking to reduce its Middle East footprint, officials familiar with the conversations said Monday.

The Houthi rebels warned foreigners to leave the area of Saturday’s attacks, which targeted installations belonging to the state-owned oil company, Aramco. The facilities could be targeted again at “any moment,” a Houthi military spokesman said.

“We assure the Saudi regime that our long hand can reach wherever we want, and whenever we want,” spokesman Yahya Saree said in a statement, adding that drones modified with jet engines were used in the operation Saturday.

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The Houthis, who seized Yemen’s capital from the internationally recognized government in 2014, have been fighting a devastating war against a Saudi-led coalition in Yemen and, according to U.S. and Saudi officials, have received military and logistics support from Iran.

Brian Hook, the State Department’s special representative for Iran, spoke with congressional staffers from the national-security committees about the situation in a call Monday afternoon. When asked about the impact of the strike on the kingdom, Hook responded that the Saudis consider it to be “their 9/11,” said two people familiar with the call.

The comparison to the terrorist attacks in the United States, in which 15 of the 19 hijackers came from Saudi Arabia, rankled several staffers, said the people who spoke on the condition of anonymity to discuss the details of a private briefing.