The Haradh border crossing, the largest for people and goods between the world's top oil exporter, Saudi Arabia, and its impoverished neighbor, was evacuated amid shelling which razed its departure lounge and passport section, witnesses said.

Residents of several Yemeni villages in the area left their homes and fled from the frontier, which has turned into a front line between the kingdom and the Iran-allied rebels.

Arab air raids hit military bases and weapons stores in the capital Sanaa and local officials said a mid-level Houthi commander, Abu Bassam al-Kibsi, was killed in an air strike in the central province of Raymah.

Saudi Arabia has led an Arab coalition bombing the Houthis and backing southern Yemeni fighters opposing the group and loyal to the exiled government in Saudi Arabia headed by President Abd-Rabbu Mansour Hadi.

The Sunni Muslim states believe the Shi'ite Houthis are a proxy for influence by their arch rival Iran, but their campaign has yet to reverse the rebels' battlefield gains.

Local fighters combating the Houthis in Yemen's south reported Saudi-led air strikes on a major air base controlled by the group in Lahj province and say they killed eight Houthi fighters in an ambush in Dalea province on Sunday.

Residents in the central city of Taiz said Houthi forces and pro-Hadi fighters fired tank and artillery shells at each other throughout the city overnight, killing five civilians.

The Houthis seized control of a military base on a strategic mountaintop in the center of the city, eyewitnesses said.

A United Nations-backed peace conference set for May 28 in Geneva remains in doubt, as Hadi's exiled government in Saudi Arabia has expressed reluctance to attend before the Houthis recognize their authority and quit Yemen's main cities.

The Houthis have demanded a ceasefire before any talks.