AL MUKALLA, Yemen — Southern fighters battling Houthi rebels seized control of the international airport in Yemen’s port city of Aden on Tuesday, dealing the Houthis their most significant defeat in the city since they stormed it more than three months ago, witnesses and security officials said.
Backed by a column of new, heavily armored vehicles, the southern fighters, who are supported by Saudi Arabia and its allies, also drove the Houthis from the nearby Khor Maksar district, site of some of the bloodiest clashes in Aden since the Houthis entered the city.
The Houthis and their allies have weathered past advances by their opponents and retained control of at least three important neighborhoods in the city, local officials said. But the sudden loss of territory was an unexpected blow to the Houthis, who have captured territory across the country despite a nearly four-month aerial bombing campaign led by Saudi Arabia aimed at forcing their retreat.
The Saudis view the Houthis, a Shiite-led group from northern Yemen, as a proxy force for Iran, Saudi Arabia’s regional rival. The Houthis, who acknowledge their close alliance with Iran, deny they are acting on Tehran’s orders.
Despite having carried out thousands of airstrikes, the Saudis have failed to achieve any of their original objectives, including restoring to power President Abdu Rabbu Mansour Hadi, who was driven into exile by the Houthis.
The gains by the southern fighters on Tuesday appeared to show a determined effort by the Saudis and their Persian Gulf allies to forcefully shift the momentum of the war in the face of intensifying pressure from the United Nations and relief agencies to pause the bombings to address a humanitarian crisis in Yemen.
Last week, the Saudis ignored a deadline for a United Nations brokered truce, saying they had received no request from Yemen’s Saudi-backed government in exile to stop the fighting.
Saudi officials might have been anticipating the push to reclaim Aden by the southern fighters, who include local militiamen, separatists who want an independent state in southern Yemen and hard-line Islamists. A local military commander said the armored vehicles had been supplied by the United Arab Emirates, which is supporting the Saudi-led offensive.
Ali al-Ahmadi, a spokesman for the local forces, said most of the fighters who took part in the assault on the Houthis on Tuesday had been trained in military camps in Saudi Arabia or in Aden.
As the fighting intensified in Aden, it seemed to further dim hopes for any imminent truce. The United Nations said Tuesday that at least 142 civilians were killed in the previous 10 days because of airstrikes and ground fighting, pushing the civilian death toll in the war to more than 1,600.
At least 25 people were killed Monday when Saudi-coalition warplanes struck a slum on the eastern edge of Sana, the capital, destroying at least nine houses, according to residents. The slum is inhabited by people who belong to a marginalized Yemeni social class referred to commonly with a pejorative: “the servants.”
“My cousins, my grandmother, all of them were killed here,” said Nasim Darwish, 20, standing near the rubble caused by the strike. Many of her neighbors, she said, “were cut to shreds.”
The Houthis and their allies, security forces loyal to former President Ali Abdullah Saleh, have been accused of imposing a brutal siege on Aden, the country’s second-largest city. In addition, airstrikes by the Saudi coalition have crippled water and electricity facilities, according to Donatella Rovera, a crisis-response adviser for Amnesty International, who has spent several days in the city. Neighborhoods away from the front line offered little protection from the fighting, she said, because rockets and mortar rounds killed residents in their homes.
“The tragedy of it all is that civilians are really caught in the middle,” she said. “There are not a lot of safe options for them.”
An earlier version of this article referred incorrectly to a resident of a slum. The resident, Nasim Darwish, is a woman.