SANA'A, Yemen - Apparent aerial bombardment hit a camp for displaced people near the Saudi border Monday, killing dozens of people, aid workers said, as a Saudi-led coalition pounded rebel positions across Yemen with airstrikes.

Panicked civilians fled Yemen's capital, Sana'a, as thunderous bombing runs, answered by antiaircraft fire, shook the city overnight and again Monday afternoon. In the country's south, rebel Shiite Muslim Houthis fought their way to the outskirts of the port city of Aden, the country's commercial hub.

Outside Aden, Houthi fighters and their allies for the first time came under naval bombardment as they advanced on the city, the Reuters news agency reported. Egypt, which last week had dispatched warships to the area, did not immediately confirm whether its forces had carried out the strikes.

Yemen has spiraled into chaos amid the Houthi offensive, which began last year but has sharply intensified in recent weeks. Sana'a fell to the Shiite Muslim rebels months ago, and the Houthis launched a major offensive targeting Aden after Western-backed President Abed Rabbo Mansour Hadi took refuge there.

Hadi was forced to flee the country last week, and most foreign embassies have been shuttered, with some Aden-based diplomats plucked to safety by sea.

In Sana'a, airstrike targets included an encampment of an elite military unit that has sided with the Houthis, located in the hills near the presidential palace, witnesses said. Other strikes took place in Marib province, east of Sana'a and home to electrical installations that power the capital, and in the country's south, according to officials and witnesses.

In Hajjah province, which borders Saudi Arabia, bombardment hit the Muzraq camp in the district of Haradh, aid workers said. Casualty counts varied, with some reports saying up to 45 people had been killed. Mogib Hassan, a spokesman in Sana'a for the U.N. High Commissioner for Refugees, reported dead and wounded numbered in the dozens, and said the agency "strongly condemned" the attacks.

A Yemeni journalist in Haradh, Mohammed Kbsi, said he believed the Saudis had mistaken the concentration of displaced people for Houthi forces. The U.N. said it was working to relocate the camp's inhabitants to a safer area.

With fighting raging across Yemen, Arab leaders meeting in Egypt over the weekend declared their intention to form a joint Arab military force in response to the Yemen crisis and other regional conflicts. Monday marked the fifth day of airstrikes by the Saudi-led coalition.