A Houthi official on Monday warned the United States it would face a “painful response” if it joined the war in Yemen, where Saudi Arabia has reportedly sought Washington's help in countering the Iran-backed group as it comes under repeated attacks.
Yemen's civil war, in which a Saudi-led military coalition backs the government against the Houthis, reignited in July, months into a wider regional conflict that has disrupted energy markets and plunged the Middle East into crisis.
The Houthis quickly began targeting Saudi oil facilities, tankers and transport hubs, including a series of deadly strikes on Riyadh's airport, putting the world's largest oil exporter under pressure.
Explosions were heard over the Saudi capital again on Monday night. The Saudi-led coalition said it had intercepted a Houthi missile, while the group claimed responsibility for another attack targeting the airport.
Later, the coalition announced that it had intercepted two ballistic missiles in the south of the kingdom, near the border with Yemen.
In a statement posted on X, the coalition said it had “intercepted and destroyed two ballistic missiles launched by the terrorist Houthi militia towards Khamis Mushait”, a city where a Saudi military base has previously been attacked.
Following a strike on Riyadh's airport on Saturday that killed 13 people, US President Donald Trump said he was considering joining Saudi strikes against the Houthis, after reportedly turning down previous requests for military assistance from the kingdom.
“The Houthis are misbehaving very badly. They're misbehaving very badly. No good,” Trump said on Monday.
“If the US becomes involved in the aggression against Yemen, we will not deliberate over the decision to respond, rather, there will be a swift and painful response targeting the US and all its interests in the region,” Mohammed Al Bukhaiti, a member of the Houthi political bureau, told AFP in an interview.
He also warned employees and workers at Saudi oil facilities and airports to stay away from the sites, saying they had become “legitimate targets”.
Saturday's strike on King Khalid International Airport was the deadliest attack on Saudi soil in more than a decade, leaving hundreds more wounded.
Trump called the attack “not acceptable” and said he would speak to Saudi Crown Prince Mohammed bin Salman, the kingdom's de facto leader. He told reporters that Washington was “going to look at” the possibility of joining Saudi strikes.
Operations at the sprawling airport on the outskirts of Riyadh remained suspended on Monday.
Bukhaiti said the campaign against Saudi targets was intended to send a message to the crown prince “that he can no longer wage aggression against Yemen from a safe position”.
Saudi Energy Minister Prince Abdulaziz bin Salman told a conference in Riyadh on Monday that the recent attacks had “tested our infrastructure, our institutions, our people, and our resilience”.
“The events of recent weeks are serious, our response must be equally serious,” he said.
CCTV footage of Saturday's attack released by Saudi authorities showed Muslim pilgrims in religious attire waiting in departure lounges before a sudden explosion tore through the building, sending flaming debris crashing down.
Tensions remained high in Riyadh on Monday, with state broadcaster Al Ekhbariya reporting that the military coalition was responding to drone and missile threats.
In the evening, mobile phones received a loud government alert warning of a “hostile aerial threat”, shortly before authorities announced the interception of the missile.
The alert delayed the start of a football match between Uzbekistan's Neftchi Fergana and Saudi club Al Nassr, which features Portuguese star Cristiano Ronaldo.
It was the first time the phone alert system had been used in Riyadh in weeks. Authorities gave no official explanation for the absence of similar alerts during attacks targeting the capital in recent days.
The Houthis also claimed to have targeted the Khamis Mushait military base in southern Saudi Arabia with a drone.
The US embassy in Saudi Arabia said American government employees must obtain its authorisation before using any airport in the kingdom. It also urged US citizens to exercise “extreme caution” if they chose to travel through the country's airports.
The embassy said American citizens had been detained for taking photographs of recent events in Saudi Arabia.
Etihad Airways, the United Arab Emirates' national carrier, announced on Monday that it was cancelling all flights to and from Riyadh until next week. It also suspended services to Dammam and Jeddah.
Bahrain's national carrier, Gulf Air, said it was cancelling all flights to Riyadh until Saturday.
US airline Delta Air Lines announced that it would postpone the launch of direct flights between Atlanta and Riyadh, which had been scheduled for October 23.
Despite massive spending on military equipment, Saudi Arabia is struggling to defend its extensive network of oil, military and transport facilities from Houthi attacks across the country's vast, predominantly desert territory.
Thomas Juneau, a security analyst at the University of Ottawa, said that despite some successes, “Saudi Arabia is so large that it's simply impossible for them to consistently defend themselves”.
Riyadh has led an international coalition providing military support to Yemen's government since 2015, including efforts to control Yemeni airspace and the airport in Sanaa, the Houthi-held capital.
Juneau said the Houthis now “want to do to Saudi Arabia what Saudi Arabia does to them”.
The protracted civil war has left Yemen, one of the region's poorest countries, grappling with a deeply entrenched humanitarian crisis.
UN human rights chief Volker Turk said he was “appalled by the repeated attacks” on Saudi Arabia but urged both sides to de-escalate.
“Continued fighting will only unleash further misery with no end in sight,” he said.