The United Nations humanitarian coordinator for Yemen says it is seeking ways for ensure unconditional access to Taiz, a city of about 25,000 residents besieged by Shiite rebels who control the capital and have been fighting an internationally recognized government.

UN humanitarian coordinator Jamie McGoldrick says Saturday in Sanaa, the capital, following a visit to Taiz that "basic services are scarce, including access to water and fuel."

Taiz has been besieged for months by Shiite rebels known as Houthis who have been indiscriminately shelling the war-devastated city and blocking the delivery of humanitarian aid, according to residents and aid groups.

Taiz, which lies on the border between northern and southern Yemen, could be a major turning point in Yemen's civil war, potentially cementing the Houthis' loss of Yemen's south.