Saudi Arabia has renewed bombing efforts against Iranian-backed Houthi forces in Yemen after a Yemeni political leader called off his alliance with the Houthis.

Saudi Arabia's bombing has created a humanitarian nightmare scenario in Yemen.

SANAA, Yemen (AP) — Yemenis in the war-torn country's capital crowded into basements overnight as Saudi-led fighter jets pounded the positions of Houthi rebels, who are now fighting forces loyal to a former president for control of the city.

Suze van Meegen, Sanaa-based protection and advocacy adviser for the Norwegian Refugee Council, said Monday that the violence left aid workers trapped inside their homes and was "completely paralyzing humanitarian operations."

"No one is safe in Sana'a at the moment. I can hear heavy shelling outside now and know it is too imprecise and too pervasive to guarantee that any of us are safe," she said.

Fighting erupted between the Iranian-allied Shiite rebels and forces loyal to Ali Abdullah Saleh last week, unraveling their fragile alliance, formed in the face of the internationally-recognized government and Saudi-led coalition.

The breakdown of the alliance has led the coalition to step up its bombing of Houthi positions, in support of Saleh's forces. Tribes who support Saleh have tried to assert control over their areas across the city.

"The night was tough," Robert Mardini, the regional director of the International Committee of the Red Cross, posted on his Twitter account. "Massive urban clashes with heavy artillery and airstrikes. Yemenis stuck in their homes, too scared to go out. Reduced access to water, health care, food and fuel."

The Houthis and forces allied to Saleh swept into the capital, Sanaa, in 2014. The Houthis dominate the northern part of the city, while Saleh's forces hold the southern part, with much of the current fighting concentrated around the Political District, home to ministries and foreign embassies. The Houthis appeared to be targeting the homes of Saleh's family, political allies and commanders.

Civilians living in the area are largely cut off from the outside world.

In southern Sanaa's Fag Attan neighborhood, the Houthis used tanks, artillery, and anti-aircraft guns to try to take out snipers loyal to Saleh, damaging or destroying several buildings.

Residents said the night was shattered by the sounds of gunfire and children screaming.

"It's like horror movies," said Bushra, a local woman who asked that her last name not be published for fear of retribution. "I have lived through many wars but nothing like this."

Witnesses said the bodies of slain civilians and fighters littered the streets, as no ambulances were able to reach the area.

It was not immediately possible to gauge the toll of the battles. Medical officials say at least 100 people have been killed and more than 300 wounded in the fighting, which began Wednesday. They spoke on condition of anonymity because they weren't authorized to speak to the press.

The Saudi-led coalition launched an air campaign against the rebels in March 2015 and later expanded into ground operations. Saudi Arabia views the Houthis as an Iranian proxy on its doorstep, and the rivalry between the two regional powers has amplified the conflict. Iran supports the Houthis but denies arming them.

The stalemated war has killed more than 10,000 civilians and displaced 3 million. Even before the fighting, Yemen was the poorest country in the Arab world. It is now on the brink of famine and grappling with a cholera epidemic.

In the latest fighting, the coalition has thrown its support behind Saleh, dubbing his fight against the Houthis a "popular uprising." Witnesses said airstrikes hit the airport and a military camp in northern Sanaa, the district controlled by Houthis.

Houthi spokesman Mohammed Abdel-Salam said the coalition is targeting Houthi positions in support of Saleh's forces, saying the coalition now has "agents in the middle of Sanaa, directing the jets of the aggression."