RIYADH - Saudi Arabia said it shot down a ballistic missile Tuesday over Riyadh fired from Yemen by Iran-backed Huthi rebels who announced that the target was the official residence of King Salman.

Saudi Arabia and the United States have accused Iran of supplying weapons to the insurgents, and Riyadh described the latest missile as “Iranian-Huthi”.

An AFP correspondent in Riyadh heard a loud explosion at 1050 GMT, shortly before the scheduled unveiling of the Saudi budget, which is usually announced by the king from the Yamamah palace, his official residence.

“The missile was aimed at populated residential areas in the Riyadh area, and - thank God - was intercepted and destroyed south of Riyadh without any casualties,” the official Saudi Press Agency quoted a spokesman for the Saudi-led coalition against the Huthis as saying.

“The possession of Iranian-manufactured ballistic weapons by terrorist organisations, including the Iran-backed Huthi militia, is a threat to regional and international security,” Turki al-Maliki added.

It was the second missile fired by the Huthis - who seized the Yemeni capital in 2014 - at Riyadh in the past two months.

“Missile force announces the launch of a Burkan (Volcano) H-2 missile against the Yamamah Palace in Riyadh,” the rebels’ official news outlet Al-Masirah tweeted.

The Pentagon said Tuesday it was working with Saudi Arabia to determine events surrounding the latest missile launch from Yemen, but it did not immediately point fingers at Iran.

“The Department of Defense is aware of recent reports that Yemen-based Huthi forces launched a ballistic missile into Saudi Arabia and that the Huthis have taken responsibility for this attack,” the Pentagon said in a statement.

It added that the US was working closely with Saudi Arabia “to fully understand what took place and to ensure that our Saudi partners have the resources they need to defend their territory against indiscriminate attacks against civilian-inhabited areas.”

At least 136 civilians have been killed over 10 days of Saudi-led air strikes on Yemen this month, the United Nations said Tuesday, with the organisation’s human rights chief decrying an “inferno” on the ground.

The UN human rights office said it had tallied 136 civilians killed and another 87 injured in the strikes on Sanaa, Saada, Al Hudaydah, Marib and Taez governorates between December 6 and 16.

“We are deeply concerned by the recent surge in civilian casualties in Yemen as a result of intensified air strikes by the Saudi-led coalition,” spokesman Rupert Colville told reporters in Geneva.

A Saudi-led coalition has been waging an air campaign against Huthi rebels since March 2015 in an attempt to shore up the internationally recognised government of Abedrabbo Mansur Hadi.

More than 8,750 people have been killed in the conflict since the intervention in the impoverished Arabian Peninsula country, where more than 2,000 people have also died of cholera this year.

The attacks, which could further escalate a military campaign by a Saudi-led coalition against the rebels, underscore how the raging Yemen conflict is increasingly spilling across the border. The first attack targeted Riyadh international airport on November 4, and triggered the tightening of a long-standing Saudi-led blockade of Yemen - already on the verge of famine. Saudi Arabia angrily accused its arch foe Iran of supplying the missile to the rebels, a charge Tehran strongly denied.

On Thursday, US ambassador to the United Nations Nikki Haley presented what she called “undeniable” evidence that last month’s missile was “made in Iran”.

But her comments went beyond the findings of a UN investigation which reached no firm conclusion on whether the missile came from an Iranian supplier, saying only that it had a “common origin” to some Iranian designs.

The coalition, which accuses the rebels of being a proxy for Iran, says the blockade is needed to stop the flow of arms to the Huthis from Tehran.

Residents in the Saudi capital reported hearing a loud explosion and seeing smoke after Tuesday’s attack.

“I was in my office when I heard a big bang,” said Tomas Kompikan, one of the many foreign workers in Riyadh. “Suddenly after around 30 to 45 seconds I heard a next sound... and we saw a white smoke.”

The Huthi rebels last month warned that they considered “airports, ports, border crossings and areas of any importance” in Saudi Arabia, as well as its ally the United Arab Emirates, as legitimate targets.

More than 8,750 people have been killed since Saudi Arabia and its allies joined the government’s fight against the Huthis in 2015, triggering what the UN has called the world’s worst humanitarian crisis.

The air strikes have intensified since the December 4 killing of ex-president Ali Abdullah Saleh at the hands of the Huthis after his alliance with the rebels collapsed.

At the same time, forces of the Saudi-backed Yemeni government have stepped up attacks on the rebels and last week retook the Red Sea town of Khokha.

A medical source in Yemen said Tuesday that 23 Huthi fighters had been killed in clashes with Saudi-backed government forces over the past day in Hodeida province on the Red Sea coast.

A military source said at least 14 pro-government fighters were killed in the same period.

The rebels were trying to recapture territory lost to government forces in the past week, including Khokha, according to another military source.

Abdul Rahman Hajri, a pro-government commander, said loyalist forces “foiled the attack”.