The U.N. is warning of famine in the Yemeni city of Taiz, which has been besieged by Shiite Houthi rebels for months.

The World Food Programme said Monday that Taiz "is in the grip of severe food insecurity at 'Emergency' level - one step below famine."

The U.N. agency says it delivered enough aid to part of the city on Saturday to support 3,000 families for one month.

The central city of Taiz has been a major battleground between the Houthis and forces allied with the internationally recognized government. The rebels are allied with army units loyal to a former president.

A Saudi -led coalition launched an air campaign against the rebels in March 2015 and has sent in ground forces. Yemen is the Arab world's poorest country.