SAMY MAGDY CAIRO — Saudi Arabia has launched an investigation to determine how its air defenses failed to intercept a barrage of missiles and drones fired by Iran-backed Houthi rebels , including an attack on Riyadh airport that killed at least 13 people and wounded over 300, two regional officials said Monday.

The officials, who spoke on condition of anonymity because they were not authorized to comment publicly, said the initial probe showed that Yemen’s Houthis first fired multiple drones to pave the way for a mix of cruise and ballistic missiles to reach Riyadh’s King Khalid International Airport.

The Houthis possess ballistic missiles and advanced systems fitted with warheads that can change direction during flight and pose a challenge to Patriot interceptors and other defense systems used by the Saudis.

One of the officials said the investigation also aims to find out why air defense systems did not provide earlier warning of the attack in which the Houthi missiles and drones flew over 1,000 kilometers (621 miles) to reach Riyadh.

The Saudi government-run Center for International Communication, which oversees foreign media, did not immediately respond to a request for comment.

On Monday, Saudi state-run media reported that its military was responding to a new attack involving drones and cruise missiles, without providing details.

The Saudis are looking to the U.S. to become more directly involved in their fight against the Houthis. The U.S. has provided intelligence sharing, target identification and planning for a Saudi-led offensive, but so far has held off on directly carrying out strikes against the Houthis.

A U.S. intervention could prompt the Houthis to try to halt shipping through the Bab el-Mandeb Strait at the southern end of the Red Sea off Yemen, restricting the flow of oil out of the Persian Gulf.

The flow of Mideast oil has already been complicated by Iranian efforts to choke off the Strait of Hormuz , another waterway through which about one-fifth of the world’s oil flowed before the U.S.-Iran war started in late February.

The rebels seized key areas along the Bab el-Mandeb last month. The Saudi-led coalition, backing forces with Yemen’s internationally recognized government, has been trying to seize them back.

U.S. President Donald Trump on Saturday told reporters after the deadly airport strike that he was looking at the possibility of carrying out U.S. attacks against the Houthis.

But the conflict also comes at a delicate time for Trump, just weeks before U.S. midterm elections that will show whether his Republican Party keeps control of Congress.

Persistent inflation and high gas prices fueled by the ongoing conflict with Iran have driven widespread American disapproval of that war. Expanding U.S. military involvement to the Saudi-Houthi conflict comes with the risk of further stoking resentment in the American electorate.

Houthi officials said that Saudi Arabia on Monday carried out new strikes on the Yemen capital of Sanaa, killing one person and wounding 12.

The Riyadh airport remained closed on Monday and workers in the capital’s financial district were told to work from home.

Yet, the Saudis on Monday continued with the second day of the World Petroleum Congress in Riyadh, even as the worsening conflict with the Houthis has put the Gulf — already shaken by the U.S.-Iran war — on edge.

More than 70 ministers, over 300 CEOs and senior executives and leaders from more than 25 international energy organizations and institutions had been confirmed to participate in the conference.

Separately, an Emirati diplomat on Monday called for “joint Gulf action” to defend Gulf countries against attacks by Iran and its allied groups.

Anwar Gargash, a diplomatic adviser to the rulers of the United Arab Emirates, said Iran and its allies wrongly assessed that Gulf Arabs were “the weakest link” in the U.S. war against Iran, during which Tehran and its allies repeatedly attacked Arab countries on the other side of the Gulf.

“It has become clear that we are all targeted, and that our security is indivisible,” he wrote on social media, adding that attacks on Saudi Arabia “undermine the security of the UAE and all Gulf states.”Iran’s Foreign Ministry on Monday expressed concern about fighting between the Saudis and Houthis and said Iran would be ready to settle disputes between them through diplomacy.

“We are severely concerned about developments in the Arabian Peninsula,” Esmail Baghaei said at his weekly briefing. “We have many times announced readiness for applying our good offices in order to facilitate talks between the two sides.”Baghaei said that Foreign Minister Abbas Araghchi and his Saudi counterpart, Prince Faisal bin Farhan Al-Saud, spoke by phone on Sunday about the situation but did not offer details.

Speaking at a conference in Abu Dhabi focused on the postwar future of the Middle East, former U.S. Secretary of State Mike Pompeo said that the deadly Houthi strikes on Saudi Arabia was a troubling development that underscored that the U.S. has not yet achieved its objectives for the war against Iran.

“What it does demonstrate is that we’ve not yet achieved deterrence. We collectively have not yet achieved deterrence,” said Pompeo, who served as secretary of state and CIA director during Trump’s first term. “You have to crush the Iranian regime, period, full stop. There’s no solution short of that.