Airstrikes and anti-aircraft fire rocked the capital, Sanaa, while Houthi rebels continued their push into southern Yemen. Meanwhile, Arab foreign ministers gathered in Egypt.
Yemen is minor producer of crude oil but controls a strategic energy waterway. More than 3.8 million barrels a day pass through the Bab el-Mandeb Strait at the southern entrance to the Red Sea.
The Saudi ambassador to Washington also says the air operations against the Shiite Houthi rebels will continue and "we will see coalition partners join in the effort."
The U.S. has lost a key base for counterterrorism operations. The proxy war between Iran and Saudi Arabia is heating up. And one more Middle Eastern state has dissolved into chaos.
The attacks, coordinated with 10 allies, began hours after rebels seized an airbase that was critical to U.S. drone operations against al-Qaida. The base is just 35 miles from Aden, an economic hub.
Britain reportedly has withdrawn its remaining special forces, days after a similar U.S. move, in response to the worsening security that the U.N. envoy for Yemen described as the "edge of civil war."
In an interview with NPR's Morning Edition, outgoing Secretary of Defense Chuck Hagel says he is concerned about the toll of repeatedly rotating the same soldiers back to the front lines.