Arab leaders vowed Saturday to back the embattled Yemeni president as a Saudi Arabia-led coalition intensified airstrikes on Shiite rebel targets across Yemen, escalating a conflict that many residents fear could lead to a land invasion.

The rebels, known as Houthis, pressed on despite the airstrikes and pounded the southern city of Aden with tank fire, witnesses reported. One politician described a situation of “great chaos” in the city, a key prize in the Yemen battle. Hospitals filled with the wounded. Dozens of diplomats fled the city.

Yemeni President Abed Rabbo Mansour Hadi slipped out of Aden and sought refuge in Saudi Arabia this past week after struggling for months to maintain power as Houthi rebels seized increasing areas of the country. The Saudis and their allies think that the Shiite rebels are backed by Iran and that Tehran is trying to exert control over a country that had been an ally of Riyadh and Washington.

Support for Hadi was firmly voiced by leaders attending the Arab League summit Saturday in the Egyptian resort town of Sharm el-Sheikh — a rare sign of unity in a region rife with divisions.

The rulers of Egypt, Bahrain, Qatar and Saudi Arabia, among others, billed Yemen’s spiral into chaos as a grave threat to the entire Middle East, and on Saturday, officials submitted a draft resolution to create a joint Arab military force to respond to the region’s growing crises.

The details of any potential security regime remained unclear. But with battles raging across Libya, Syria, Iraq and Yemen, the show of Arab support for the anti-Houthi offensive underscored a readiness by regional states to interfere in neighboring countries beset by violence.

“The Arab nation has passed through many phases, none of which has posed as much of a threat as the one we’re experiencing now,” Egyptian President Abdel Fatah al-Sissi told the summit.

King Salman of Saudi Arabia, in another speech to the delegates, vowed to continue military operations in Yemen “until stability is returned,” a reference to restoring Hadi’s authority.

The Saudis are leading a coalition of about 10 countries that have pledged warplanes and ships to the Yemen fight. Several countries, including Egypt, have said they are prepared to commit ground forces to the operation if necessary.

Yemen’s foreign minister, Riyadh Yaseen, told reporters at the summit that it was “very possible” that ground troops would be required to push back the rebels, Reuters reported.

Hadi also addressed the summit, expressing his approval of the coalition attacks that began Thursday and declaring that the military operation “must continue.” He characterized the rebels who effectively toppled his government in Sanaa in February as “stooges” of Iran.

The remarks highlighted the escalating tensions between the region’s major rivals: Sunni Saudi Arabia and Shiite Iran. Tehran has increased its support for the Houthis, who follow the Zaydi sect of Shiite Islam. The Saudis and Iranians are already backing warring parties in other destructive regional conflicts such as the Syrian civil war.

Yemen, the poorest Arab country, has struggled not only with the conflict between the Shiite rebels and pro-government forces, but also with attacks by al-Qaeda in the Arabian Peninsula. In addition, a Yemeni wing of the Islamic State claimed responsibility for suicide bombings this month that killed nearly 140 people in the capital.

Residents of Sanaa, Aden and the western province of Hodeida said the frequency of airstrikes increased late Friday and early Saturday, with the targets including military installations controlled by the Houthis as well as military units loyal to Ali Abdullah Saleh, a longtime Yemeni strongman who was forced from power in 2012. Saleh is widely believed to have allied with the Houthis during their takeover of Sanaa in September and the rebel offensive that has brought the insurgents to the northern outskirts of Aden.

Riad Kahwaji, head of the Dubai-based Institute for Near East and Gulf Military Analysis, said the coalition attacks have targeted air defenses, arms depots and communications lines that support the Houthis. The intention, he said, is to “prepare the way” for an “imminent ground offensive.”

“It’s a classic move of taking out air defenses, ensuring air superiority and taking out command-and-control and communication posts,” he said. Houthi forces would likely crumble in the face of a ground assault by militaries such as Egypt’s, which are more organized and heavily armed and have received significant U.S. assistance, Kahwaji added.

Lina Khatib, director of the Carnegie Middle East Center, said the Houthis would struggle to repel a ground offensive in places like Aden and the southern city of Taiz, in part because of a lack of support from local populations. The Houthis are from the north, which has long been dominated by their fellow Zaydi Shiites, unlike the predominantly Sunni south.

“I think they’re losing this battle,” Khatib said of the Houthis, adding that Iran would likely hesitate to come to the rebels’ defense in the event of a Saudi-led ground assault.

“They are useful allies of Iran, but they are not seen as indispensable by Iran,” she said.

Airstrikes early Saturday smashed into the Attan air base in the capital for a second straight day, residents said, producing massive fireballs that lit up the sky.

In western Hodeida province, residents said that at least two air-defense systems had been attacked, including one located near a port facility. Yemeni officials and Houthi opponents claim that Iranian weapons have been shipped to the rebels throughout the area. Houthi officials deny receiving Iranian weapons.

In Aden, one attack apparently carried out by the Saudi-led coalition on an ammunition depot next to the city killed and wounded scores of people, according to residents and physicians.

Al-Khadher Laswar, general manager of the Health Ministry office in Aden, said nine people suffered third-degree burns in the attack and five others were injured by falling debris. He said he had no accurate figures on the number of people killed because the risk of secondary explosions made it too dangerous to approach the site.

He added that 61 people were killed and nearly 500 wounded in clashes in Aden and surrounding areas in recent days. Aden residents say that Houthi rebels and pro-Saleh military units control the city’s airport, and they also cite rising lawlessness that has resulted in looting.

Basem al-Hakimi, a politician in Aden who opposes the Houthis, described the situation as chaotic. “Everyone is trying to get weapons to fight the Houthis. It’s madness,” he said.

The Saudi Press Agency reported that the desert kingdom’s navy had evacuated 86 diplomats from Aden.

Video footage showed people looting what appeared to be Hadi’s abandoned residence in Aden. A voice-over said, “This is the house of Abed Rabbo Mansour Hadi,” as looters were seen carrying off items such as living room chairs.

Qasem Dawood Ali, a worker at a nongovernmental organization in Aden, said bodies were lying in the streets as hospitals filled with the wounded.

“Right now there is heavy bombing from Houthi tanks near the airport and you can also hear the explosions coming from the weapons-storage facility,” he said by telephone. “Aden is falling apart.”

Naylor reported from Beirut. Erin Cunningham in Cairo and Heba Habib in Sharm el-Sheikh contributed to this report.