The United Nations refugee agency says tens of thousands of people have been displaced as fighting intensified along Yemen's western coastline.

UNHCR spokesman William Spindler says 34,000 people fled their homes after fierce fighting erupted in the port towns of Mokha and Dhubab on the Red Sea.

He said on Friday that the majority of the displaced are headed to the outskirts of the war-torn city of Taiz in western Yemen.

Yemeni forces allied with the internationally recognized government of President Abed Rabbo Mansour Hadi have recently seized Mokha and plan to push northward.

Yemen's Shiite Houthi rebels captured the capital, Sanaa, in 2014, triggering a war in which a Saudi-led coalition is waging an extensive air campaign.

Much of Yemen's infrastructure is destroyed; thousands of civilians have died.