The United States warned Saturday that hostilities between Saudi Arabia and Iran-backed Houthis could "escalate rapidly" after a missile attack targeted Riyadh for the first time since the Yemen conflict resumed.

U.S. President Donald Trump cut short a weekend at Camp David to return unexpectedly to the White House, as tensions rose in the Middle East.

Explosions were heard in Riyadh early Saturday, AFP journalists reported, after Saudi authorities issued their first air raid alert in the capital since fighting returned to neighboring Yemen.

As Houthi rebels closed in, Eshraq Abdel Gelil and her husband fled their home, walking through the mountains before catching a ride to a nearby city. Four months pregnant, she feared another miscarriage.

They are among an estimated 125,000 people who have fled as the Iran-backed rebels have advanced down the Red Sea coast to a key maritime chokepoint. The offensive, linked to the wider Iran war, has threatened Saudi oil exports, pushed up global fuel prices and rattled markets.

A former Syrian military official convicted of torturing prisoners during the rule of former President Bashar Assad was sentenced Thursday to 60 years in a U.S. prison after a federal judge recounted the "unimaginably cruel" details of his abuse.

A jury in March found Samir Ousman Alsheikh guilty on all six counts including torture and conspiracy to commit torture for his actions while in charge of Syria's infamous Adra Prison from roughly 2005 to 2008.

It's been a week since Yemen's Iran-backed Houthi rebels stormed down the Red Sea coast, extending their reach to a key maritime chokepoint and threatening Saudi Arabia's oil exports.

The Houthis' biggest land grab in years reignited Yemen's 12-year civil war and pushed up global fuel prices. It also gave Iran another potential source of leverage as the United States has started to loosen Tehran's grip on the Strait of Hormuz, on the other side of the Arabian Peninsula.

The deadly collapse of a multistory building in Gaza has drawn new attention to the hardships facing Palestinians there nearly a year after a ceasefire between Israel and Hamas promised to kickstart reconstruction.

But as talks faltered, plans for rebuilding stalled. Israel bars entry of almost all construction materials, making even repairs difficult. Many residents have since moved back into some of the hundreds of thousands of homes damaged by the war despite the risk of weakened foundations and unstable walls suddenly giving way.

Hundreds of thousands of Iranians rallied Friday in a government-organized show of defiance after months of war, pledging their readiness to take up arms in the biggest such demonstration since the United States and Israel attacked in February.

Iran's government has sought to rally the people and stress national unity, even as the economy worsens under a U.S. naval blockade of Iranian ports and new U.S. sanctions meant to increase Tehran's economic pain.

A tanker was struck in the Strait of Hormuz on Friday, causing a fire that was extinguished, according to the United Kingdom Maritime Trade Operations (UKMTO).

"The CSO of a vessel has reported a tanker being hit by an unknown projectile, causing a fire onboard which has since been extinguished," the maritime monitor said, adding that the crew were safe, although the environmental impact of the attack was "unconfirmed".

Lebanon's judiciary has accused 14 Lebanese and Syrians, including a Hezbollah member and an Assad-era Syria officer, of forming and training groups to launch attacks in Syria, a judicial official said Thursday.

Earlier this month, Lebanese authorities arrested a group including a former Syrian intelligence officer and several accomplices who allegedly planned attacks against the forces of Syria's new government and received training from Iran-backed Hezbollah. The group has denied the allegation.