Residents in Saudi Arabia's capital say they have heard new explosions in Riyadh

New explosions have been heard in the Saudi capital of Riyadh, residents said Wednesday, as blame again quickly fell on Iran-backed Houthi rebels in neighbouring Yemen.

The Saudi-led military coalition fighting the Houthis said it intercepted a ballistic missile fired by the rebels toward Riyadh. There were no immediate reports of casualties or damage.

There was no immediate comment from the Houthis, who have repeatedly targeted airports, military facilities and oil infrastructure in the kingdom in the latest front in the Iran war. Separately, the rebel-run Health Ministry reported two dead in attacks in Yemen on Tuesday and blamed the Saudis.

The Houthis, hardened by years of civil war, have emerged as Iran's most effective armed proxy of the moment, but experts say they also have their own agenda. Either way, they are applying increasing pressure on a key US ally.

Trump faces questions over possible US intervention

The sight of smoke rising from some of Saudi Arabia's most sensitive facilities has rattled the region and global markets, increasing questions for President Donald Trump, who has said he is evaluating whether the US should join the Saudi strikes on the Houthis.

The Riyadh residents spoke about the latest blasts on condition of anonymity for their safety. One lives in northern Riyadh, where King Khalid International Airport, targeted multiple times in the past week with strikes that have killed 17 people and hurt over 300 more, is located.

The Saudi civil defence reported air raid alerts in Riyadh and Kharj province southeast of the capital. Kharj is home to the state-owned Military Industries Corporation and Prince Sultan Air Base.

The Houthis have been warning in advance of attacks on both airports and oil facilities, and airlines have been suspending operations and pulling out planes. On Tuesday, a fire broke out in an administrative building at a facility operated by Saudi Aramco, one of the world's largest oil companies, in the latest targeting of the world's top oil exporter.

Experts say Saudi Arabia can't intercept everything

The escalation has highlighted Saudi Arabia's struggle to intercept Houthi missiles and drones, and the kingdom's efforts to press allies like the United States for more military support. Regional officials say that Saudi Arabia, the world's top purchaser of American weapons, is running low on interceptors.

The Saudis are trying to intercept daily attacks across a territory about three times the size of Texas. Experts have said trying to intercept all of the missiles and drones is impossible.

The Houthis have a large arsenal capable of striking targets well over 1,600 kilometres away. Some warheads change direction during flight.

Even interceptions are a danger. Overnight, Saudi Arabia's Civil Defence said debris from two intercepted Houthi ballistic missiles fell on residential areas in Riyadh, injuring four people including a child and damaging 15 homes.

Saudi-led coalition intensifies strikes on Houthi-held areas

Meanwhile, the Saudis have been carrying out airstrikes in rebel-held areas of Yemen in support of the country's internationally recognised government. The fighting erupted this year when the rebels blamed the Saudis for a strike on the airport in rebel-held Sanaa. That attack revived anger over a Saudi blockade of the Houthis. The rebels in turn declared their own blockade against the kingdom.

A week and a half ago, the Saudi-led coalition responded with a major military offensive.

On Wednesday, the Houthi-run Health Ministry said two people were killed in an airstrike Tuesday in the Ras Isa port area in Hodeida province. The strike hit a facility of the state oil company and wounded two others, the ministry said, and blamed Saudi Arabia. The Saudi-led coalition also attacked an oil facility in Sanaa.

The targeting of fuel storage facilities in Houthi-controlled areas marks a new phase in the Saudi-led coalition's campaign, said Ahmed Nagi, senior Yemen analyst at the International Crisis Group, a think tank. He added that in a war of attrition, the rebels could risk losing much of their military capacity.

“The Houthis are betting on pressure, while the Saudis are betting on time. The Houthis are trying to strike critical infrastructure in Saudi Arabia to raise the cost of continued military intervention and support for the Yemeni government,” Nagi added.