An attack on King Khalid International Airport in the Saudi capital of Riyadh killed 12 people and wounded more than 300, civil aviation authorities said early Sunday, adding that some of the injured were in critical condition.

It was the deadliest strike in any Gulf Arab country since the start of the Iran war, whose fronts have widened to include a recent surge in fighting between the Iran-backed Houthi rebels in Yemen and the Saudi-backed government forces opposing them.

The authorities' statement did not assign blame for the attack. It said the dead included four Saudi citizens, two Bangladeshi nationals, a Palestinian, a U.S. citizen, an Egyptian, a Jordanian, a Syrian and a Sudanese, and that the wounded were being treated at several hospitals.

The strike was the latest of several over the past week on King Khalid International Airport; earlier attacks there had killed four people. The escalation is expected to increase Saudi pressure on allies, including the United States, to provide military support to the kingdom.

Shortly after Saturday afternoon's attack, President Donald Trump said he was evaluating whether the U.S. should join Saudi strikes against the Houthis. “We may. We're going to look at it,” Trump said. “We just found out about the recent attack. So we'll make a decision. We move very quickly.”

A missile struck an airport complex housing terminals 3 and 4, which serve domestic flights, according to a regional official who spoke on condition of anonymity because they were not authorized to brief the media.

The surge in attacks—targeting other Saudi airports as well as military facilities and oil infrastructure—has unfolded in the week since a Saudi-led coalition launched a major military offensive against the Houthis. The rebels issued no immediate statement, though earlier on Saturday they accused Saudi Arabia of striking Sanaa International Airport in the Houthi-held Yemeni capital. The group at times takes days to claim responsibility.

Civil aviation authorities had earlier announced that airport operations were suspended, and an official notice to aviators said the suspension would run through midnight. A heavy police presence ringed the airport, all entrances were blocked and lights around the complex were dimmed. Flights were diverted elsewhere, according to the Flightradar24 tracker. Governments including the United States, Britain, Germany, Australia and Canada warned citizens to avoid the airport before their statements turned to condolences.

Later on Saturday, the Saudi-led coalition said a projectile had fallen near King Fahd International Airport in Dammam and that a Houthi-launched ballistic missile had been intercepted in Al-Kharj governorate, southeast of Riyadh.

The attacks on Saudi Arabia, the world's top oil exporter, have rattled markets and the wider region. Even so, hours after the latest strike, the Saudi energy ministry was still promoting a major international energy conference scheduled to open in Riyadh on Sunday.

Fighting between the Houthis and Saudi-backed Yemeni government forces has escalated, with the coalition providing air support to government troops trying to reverse recent Houthi gains along Yemen's Red Sea coast. Those gains have given the rebels better surveillance of shipping along a corridor that serves as a crucial alternative to the Strait of Hormuz, where Iran has been attacking vessels.

The Houthis have told the AP and other outlets that they target only Saudi shipping as part of a blockade in retaliation for one imposed on them, but concerns about wider attacks persist. The group previously attacked other ships after the war in Gaza began, describing the campaign as solidarity with Palestinians; a U.S. bombing campaign sharply curtailed those assaults.

Saudi Arabia is running low on missile interceptors and has asked France, Britain, Pakistan and Egypt to deploy air defense support to the region, regional officials told the AP last month. One official noted that the U.S. has seen its own stockpile dwindle during the war with Iran. American assistance to date has included intelligence sharing, target identification and planning for the latest offensive against the Houthis, officials have said.

Earlier on Saturday, Saudi Arabia said its foreign minister and his Omani counterpart spoke by phone about the importance of “supporting diplomatic solutions to de-escalate tensions” in the region. Oman, which lies across the Strait of Hormuz from Iran, has at times played a mediator role.

The Houthis this week warned global airlines “for the last time” about the potential consequences of operating in Saudi airspace, which they described as a theater for their military operations. Before the latest attack, Air India, FlyDubai, Lufthansa Group and Pakistan International Airlines were among the carriers suspending flights to and from Riyadh and other Saudi airports for varying periods.

The European Union Aviation Safety Agency had expanded its guidance on Saudi airspace, citing the Houthis' ability to strike targets deeper inside the kingdom, including Riyadh, and a “greater focus on aviation infrastructure.” The missile and drone attacks and interception efforts “create an increased risk of misidentification of civil aircraft,” the agency said.

Two regional officials said Houthi attacks on the Riyadh airport on Thursday had damaged three planes; they also spoke on condition of anonymity because they were not authorized to brief the media. The Saudi national carrier said one of its aircraft was damaged while it was on the ground, with no passengers aboard.

Meanwhile, Saudi authorities warned the public this week that “filming, publishing or sharing information related to countering missiles and drones and their impact sites exposes you to legal liability.”

This story was originally featured on Fortune.com.