SANA'A, Yemen - 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 last week, after struggling for months to maintain power as Houthi rebels seized increasing areas of the country. The Saudis and their allies believe 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 Yassen, 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 called Shiite rebels who forced him to flee the country "puppets of Iran," directly blaming the Islamic Republic for the chaos.

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.

Meanwhile, a news report on the Houthi-affiliated Al-Masirah television station referred to Hadi as a "puppet" of Saudi Arabia. Ali al-Emad, a senior official of the Houthi movement's political arm, Ansar Allah, told the station that nothing said at the summit came as a surprise. Saudi Arabia, he claimed, was taking charge of the Yemen issue, deciding alone what needed to be done.

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 Sana'a, 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.

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 early evening sky.

The United Nations withdrew its remaining personnel from Sana'a, dashing whatever hope remained that the fighting would stop and U.N.-sponsored peace talks would resume.