DUBAI, United Arab Emirates — An Arab military coalition invaded Yemen’s main Red Sea port on Wednesday, worsening what is already the world’s most severe humanitarian disaster by disrupting the delivery of food and other supplies to millions of Yemenis.

The air and ground attack by forces loyal to Saudi Arabia and the United Arab Emirates was aimed at tipping the balance in Yemen’s long-running civil war and driving Iranian-backed rebels out of the port of Al Hudaydah. Although fighting appeared to be limited to the outskirts of the city on Wednesday, the prospect of sustained fighting there stands to produce one of the bloodiest urban battles of the war, deepening what is already a catastrophic humanitarian situation.

After years of war, eight million of Yemen’s estimated 28 million people are at risk of starvation, according to the United Nations and aid agencies.

A protracted battle for Al Hudaydah could rival the fighting that ravaged Aleppo, Syria, or Mosul, Iraq, cities that have come to symbolize the brutality of warfare in the Middle East, according to humanitarian workers and diplomats. About a quarter of a million people in Al Hudaydah, a city of 600,000, are in danger of injury or death in an urban assault, the United Nations said.