Medical authorities speaking on the condition of anonymity claimed a Shiite rebel attack Sunday killed 45 and injured 120 north of the Yemeni port city of Aden, the Associated Press reported.  The attack came three days after a Saudi Arabia-led air and ground offensive drove the rebels from key positions in the city, including the airport. Yemen's exiled government declared the city "liberated," and the rebels vowed to strike back.

Since civil war broke out four months ago, more than 3,500 people have died in Yemen, with fighting centered around the strategic city of Aden. Food and fuel have run short, and thousands of civilians have fled.

Known as Houthis, the Shiite rebels took power in Yemen's capital Sanaa in January. Two months later, an Arab coalition led by the country's northern neighbor Saudi Arabia began a campaign to retake the nation and return its exiled government to power. The U.S. has participated in the campaign. 

However, Sanaa remains under Houthi control.