A Houthi spokesman, writing on Twitter, said the missile, known as a Volcano H-2, was aimed at a royal palace in Riyadh, Saudi Arabia. (Faisal Al Nasser/Reuters)

Saudi Arabia said Tuesday it intercepted a ballistic missile south of its capital that was fired by a rebel group in neighboring Yemen, raising regional tensions amid Saudi claims that Iran is behind a string of similar attacks while supplying the rebel fighters with weapons.

The attempted missile strike marked the second time that the rebels, known as Houthis, have targeted Riyadh since early November in retaliation for Saudi-led attacks seeking to break the rebels' grip on parts of Yemen.

Col. Turki al-Malki, a spokesman for the Saudi-led coalition, said in a statement that the missile was heading toward "populated residential areas" when it was intercepted and destroyed south of Riyadh. Witnesses described hearing a loud boom, and images on social media showed a plume of smoke in the sky.

A Houthi spokesman, writing on Twitter, said the missile, known as a Volcano H-2, was aimed at a royal palace in Riyadh.   

The immediate backdrop to the attack was the nearly three-year-old war in Yemen between the Houthis and a Saudi-led military coalition backed by the United States. The conflict has killed more than 10,000 people, displaced millions, sparked one of the worst cholera outbreaks in history and led to fears of a famine in Yemen, the Arab world's poorest country.

But increasingly, the conflict is seen as a proxy battle pitting Saudi Arabia and its Western allies against Iran, raising fears that developments in Yemen could escalate into a wider regional conflict. Saudi and U.S. officials have sought to portray the Houthi missile attacks as distinct from Yemen's civil war, framing them instead as part of what they say is Iran's unprovoked and aggressive expansion in the Middle East.  

The fighting in Yemen has only intensified in the past few weeks. 

The Saudi-led coalition and its affiliates on the ground, sensing an opportunity, have mounted a multipronged offensive on Houthi-held territory. They were emboldened by the breakdown this month of a wartime alliance between the Houthis and Yemen's former president, Ali Abdullah Saleh, that may have weakened the rebel side. Saleh, who ruled Yemen for more than three decades, was killed by Houthi fighters Dec. 4. 

On Tuesday, the U.N. human rights office said it was "deeply concerned" by an increase in civilian casualties, adding that it had verified the deaths of 136 "civilians and noncombatants" in Saudi-led coalition airstrikes in a 10-day period beginning Dec. 6. Houthi militants were also responsible for revenge attacks against members of Saleh's political party, killing at least four people in December and possibly carrying out other summary killings, the United Nations said.  

Saudi and U.S. officials have accused Iran of supplying the Houthis with weapons, including ballistic missiles fired across the Saudi border — a charge that Iran has denied. 

The Trump administration, meanwhile, has tried to use the accusations of weapons transfers to intensify international pressure on Iran.

Last week, in a news conference that included a display of missile remnants, Nikki Haley, the U.S. ambassador to the United Nations, said the weaponry amounted to "undeniable" proof of Iran's deepening involvement in Yemen.

"This evidence demonstrates a pattern of behavior in which Iran sows conflict and extremism," she said. 

In early November, the Houthis fired a missile toward Riyadh's international airport. No casualties were reported, but there were conflicting claims about whether the projectile had been shot down.

Saudi officials, as well as President Trump, said at the time that the missile was intercepted.  

According to the Defense Department, the missile fragments recovered — including remnants from the November attack — bore no indications that the missiles were shot down with a U.S.-made Patriot missile defense system, which is part of the Saudi arsenal. But not all of the missile fragments were retrieved.

The powerful Saudi crown prince, Mohammed bin Salman, called the Nov. 4 missile strike an "act of war." And after the attack Tuesday, Malki, the Saudi military spokesman, reiterated accusations that Tehran was responsible.

Separately, Saudi officials claimed Dec. 1 that their defenses intercepted another missile fired from Yemen. That assertion also could not be independently verified.

Iran has decried the Saudi-led attacks in Yemen but denied providing any military assistance to the rebels. Saudi Arabia accuses the Shiite-led Houthis of serving as a proxy force for Iran, the region's Shiite power.

Iran's envoy to the United Nations, Gholamali Khoshroo, said last week that Haley was pushing "fake and fabricated" evidence, and he denounced what he called the "irresponsible, destructive and provocative role" of the United States in the region, according to a statement carried by Iran's state-run Islamic Republic News Agency.

Haley argued that Iranian weapons shipments violate several U.N. Security Council resolutions, including the one that enshrined the 2015 nuclear deal between Iran and six world powers. International legal experts have debated whether the allegation, if true, constitutes a clear-cut violation.

Missy Ryan and Brian Murphy in Washington contributed to this report.