AL MUKALLA, Yemen — Dozens of civilians were killed when, according to aid workers and officials, what appeared to be an airstrike hit a camp for displaced families in northern Yemen on Monday. It was thought to be the deadliest single episode involving civilians since Saudi Arabia began a military campaign to drive back the Houthi movement five days earlier.

The deaths, in the Al-Mazraq camp, came as the Saudi-led Arab military coalition intensified attacks across Yemen, bombing multiple targets including a missile depot in the capital, Sana, that erupted in a nighttime conflagration and sent civilians in a nearby village fleeing the explosions, according to witnesses.

Saudi officials have framed their military offensive as an effort to roll back the gains of the Houthis, whose fighters have seized control of much of Yemen over the last seven months, and to restore to power the exiled government of President Abdu Rabbu Mansour Hadi. The Saudi offensive has been primarily driven by a fear of Iranian influence in the region: the Houthis, who practice a strain of Shiite Islam and are supported by Iran, have been accused by Saudi officials as acting as an Iranian proxy force.

Yet the military action, which has come with the threat of a ground invasion by Saudi and other Arab troops, has raised concerns that it will only further destabilize Yemen, the region’s most impoverished country as well as a haven for a powerful Al Qaeda affiliate.

Already, the chaos has caused the Obama administration to withdraw its last remaining counterterrorism advisers from Yemen. As the Saudi-led coalition has tightened its military grip on the country — restricting access by sea and air, while widening its airstrikes — there are growing fears of a humanitarian emergency, according to aid workers.

In Riyadh, the Saudi capital, a spokesman for the military coalition told reporters that naval forces were blocking the movement of ships to thwart weapons and fighters from entering or leaving. Al Ahram, the main Egyptian state newspaper, said warships from Egypt, part of the Saudi coalition, were shelling Houthi fighters to stop their advance into Aden, the southern port that is one of the last refuges of fighters loyal to Mr. Hadi.

By nighttime, huge explosions were seen rocking Sana, in what witnesses described as Saudi airstrikes on caches of missiles in a military base on a mountain — presumably to prevent the Houthis from using them. Images of fireballs from the bombings were posted on Twitter and other social media forums. It was not immediately clear whether the blasts caused any casualties.