Yemen’s civil war — in which a Saudi-led military coalition supports the government against the Iran-backed Houthis — reignited in July, months into the wider regional conflict that has roiled energy markets and plunged the Middle East into risis.

A Houthi official on Monday warned the US it would receive a “painful response” if it entered the war in Yemen, where Saudi Arabia has reportedly requested Washington’s help in dealing with the group as it weathers repeated attacks.

Yemen’s civil war — in which a Saudi-led military coalition supports the government against the Iran-backed Houthis — reignited in July, months into the wider regional conflict that has roiled energy markets and plunged the Middle East into risis.

The Houthis quickly began targeting Saudi oil facilities, tankers and transport hubs, including a string of lethal strikes on Riyadh’s airport, rocking the world’s top oil exporter.

Blasts resounded over the capital again on Monday night, with the Saudi coalition saying it had intercepted a Houthi missile and the group saying it had again targeted 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 come under attacks.

Following an attack at the Riyadh airport on Saturday that killed 13 people, US President Donald Trump said he was considering joining Saudi strikes against the group, after having reportedly rebuffed previous requests for help 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,” Houthi political bureau member Mohammed Al Bukhaiti told AFP in an interview.

He also warned “all employees and workers at Saudi oil facilities and airports to stay away from these sites, as they have become legitimate targets”.

Saturday’s strike on King Khalid International Airport was the deadliest attack on Saudi soil in more than a decade, and also left hundreds wounded.

Trump said the attack was “not acceptable” and that he would be speaking to the kingdom’s de facto leader Crown Prince Mohammed bin Salman, telling reporters the US was “going to look at” the possibility of joining Saudi strikes. 

Operations remained suspended at the sprawling airport on Riyadh’s outskirts on Monday.

– ‘Serious’ response –

Bukhaiti said the purpose of the campaign against Saudi targets was 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 events had “tested our infrastructure, our institutions, our people, and our resilience”.

“The events of recent weeks are serious, our response must be equally serious.”

CCTV footage of Saturday’s attack released by Saudi authorities showed Muslim pilgrims in religious attire waiting in departure lounges before a sudden blast tore through the building and brought down flaming debris.

The atmosphere in Riyadh remained tense on Monday, as state broadcaster Al Ekhbariya said 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” before the announcement of the interception. 

The alert delayed the kickoff of a football match between Uzbekistan’s Neftchi Fergana and Saudi team Al Nassr, home to Portuguese superstar Cristiano Ronaldo.

It was the first use of the phone alert system in Riyadh in weeks, with no official reason given for the lack of messaging during the attacks targeting the capital in recent days. 

The Houthis said they had also targeted the Khamis Mushait base in the kingdom’s south with a drone.

– Flights suspended –

The US embassy in Saudi Arabia said US government employees must obtain its authorisation before using any airport in the kingdom, and urged US citizens to “take extreme caution” if they chose to do so.

The mission also said “American citizens have been detained for taking photos of recent events” in Saudi Arabia.

The UAE’s national carrier Etihad Airways announced on Monday that it was cancelling all flights to and from Riyadh until next week, and also suspended flights to Dammam and Jeddah.

Bahrain’s national carrier Gulf Air said it too was cancelling all Riyadh flights until Saturday.

US operator Delta announced it would delay the launch of direct flights from Atlanta to Riyadh, scheduled for October 23.

Despite vast spending on military hardware, the Houthi attacks on oil, military and transport facilities across the large, mostly desert country are stretching Saudi defences.

Thomas Juneau, security analyst at Ottawa University, said that despite some success, “Saudi Arabia is so large that it’s simply impossible for them to consistently defend themselves”.

Riyadh leads an international coalition that has supported Yemen’s government militarily since 2015, including by seeking to exert control over Yemeni airspace and the airport in the Houthi-held capital Sanaa.

Juneau said the Houthis now “want to do to Saudi Arabia what Saudi Arabia does to them”.

The long-running Yemeni civil war has created a deeply entrenched humanitarian crisis in the impoverished country.

UN rights chief Volker Turk said he was “appalled by the repeated attacks” on Saudi Arabia, but urged both sides to back down, adding “continued fighting will only unleash further misery with no end in sight”.