By Mohammed Ghobari and Mohammed Mukhashef
SANAA/ADEN (Reuters) - Warplanes attacked Houthi militia in control of Yemen's largest air base north of Aden on Tuesday, seeking to expand territorial gains made by Saudi-led coalition forces since they captured the southern port city last week.
Witnesses said big explosions were heard at the al-Anad base, 50 km (30 miles) from Aden, which has been held by the Iranian-allied Houthi movement for much of a fourth-month-old civil war and commands the approaches to Aden.
A Saudi-led Arab coalition allied with southern secessionist fighters retook much of Aden last week in the first significant ground victory in their campaign to end Houthi control over much of Yemen and restore exiled President Abd-Rabbu Mansour Hadi.
Once one of the world's busiest ports, Aden sits near the Bab al-Mandab shipping lane, a major energy gateway for Europe, Asia and the United States via the Red Sea and the Suez Canal.
A ceasefire called by the coalition to start on Sunday evening fell apart almost immediately, posing problems for relief organizations seeking to expand deliveries of emergency aid amid severe shortages of food, fuel and medicine.
Reporting an apparent "friendly fire" incident, the Southern Resistance movement said in a statement that an unidentified plane had killed 12 of its fighters and wounded 40 near al-Anad on Monday, and asked the coalition to investigate urgently.
The resistance is a collection of southern secessionist forces who have received training from Gulf military instructors provided by the Saudi-led coalition in recent weeks, an effort that appears to have helped in the recapture of Aden.
In London, Oxfam said more than six million people in Yemen were on the verge of starvation, adding that months of war and a blockade on imports were pushing an additional 25,000 people into hunger every day.
The International Red Cross and Red Crescent Movement said the past two months had seen an increasing number of attacks against health-care workers and relief personnel.
It said that unidentified assailants had shot and killed two people inside an ambulance clearly marked with Yemeni Red Crescent Society insignia in central Taiz city on July 23.
Meeting his military commanders in Riyadh, Hadi paid tribute to what he called the forces of the popular opposition and their role in recpaturing Aden from the Houthis, according to a report on his sabanew.net website.
Hadi called for all regions and cities to be freed from control by the Houthis and allied army units loyal to influential former president Ali Abdullah Saleh.
In Geneva, a spokesman for the World Health Organization, said that according to data from health facilities in Yemen, 3,984 people had been killed and 19,347 had been injured between March 19 and July 19.
(Additional reporting by Omar Famy, Tom Miles and Reem Shamseddine, Writing by William Maclean, Editing by Ralph Boulton)