The White House is warning that 21 million Yemenis need emergency humanitarian help following an attack on a critical port.

The western port city of Hodeida was hit with airstrikes Tuesday night amid ongoing fighting pitting Shia rebels known as Houthis and troops loyal to the former president against Sunni militants and troops loyal to President Abed Rabbo Mansour Hadi.

White House spokesman Alistair Baskey says the port was a crucial lifeline for food, medicine and fuel for Yemen. He's calling for all parties to allow relief supplies to flow into Yemen unimpeded.

Baskey says the humanitarian situation is deteriorating and that the U.S. is deeply concerned.

The United Nations has said fighting around major ports has stalled deliveries of food and aid and impeded access to the country's interior.