REUTERS - Yemeni forces allied with a Saudi-led coalition fought Houthi militia for control of the country's largest air base north of Aden on Sunday, local residents said, hours before a humanitarian truce declared by the coalition was meant to start.

The al-Anad base, 50 km (30 miles) from the major southern port city, has been held by the Iranian-allied Houthi movement for much of a fourth-month-old civil war, and is regarded as a strategic asset commanding the approaches to Aden.

The Arab coalition on Saturday announced a ceasefire to take effect at 11.59 p.m. (2059 GMT) on Sunday evening for five days to allow for the delivery of humanitarian aid.

But the truce was cast into doubt when Houthi leader Abdel-Malek al-Houthi was reported to have rejected it, arguing it would benefit only militant groups Islamic State and Al-Qaida.

"The battle goes on and the war is not over," al-Houthi was quoted as saying in a message posted on the group's Twitter account. The Iranian-allied Houthi movement accuses its Saudi-supported foes of being in cahoots with Islamist militants like Al-Qaida, something the coalition denies.

A spokesperson for the Houthis was not immediately available for comment on the posting.

Houthi forces held up 16 trucks carrying humanitarian aid from the World Food Programme through Yemen's Al Hudaydah province to support displaced persons in the major city of Taiz.

Four months of air raids and war have killed more than 3,500 people in the Arabian Peninsula state. Aden has suffered especially, with severe shortages of fuel, food and medicine.

The 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.

Houthi fighters and army units loyal to former president Ali Abdullah Saleh captured Aden at the outset of the war, prompting Hadi to flee to Saudi Arabia, an ally along with the United States.

Aden and other southern provinces have been largely inaccessible to UN food aid, and about 13 million people -- over half the population -- are thought in dire need of food.

Warplanes attack

Coalition warplanes carried out raids near Sanaa late on Saturday and shortly after dawn on Sunday, residents reported, adding that the targets included a military base near the city.

In the city itself, a bomb exploded underneath a passenger bus, killing three people and wounding five in the southern district of Dar Selm, police said. No further details were immediately available.

Ali Ahmedi, a spokesman for anti-Houthi forces in Aden, said they continued to fight Houthi forces at the al-Anad base and had damaged aircraft, tanks and equipment stationed there.

Residents said forces of the so-called Southern Resistance, a secessionist movement allied with the coalition, had taken and Sabr, a northern district of Aden. The residents reported 25 Houthis and 10 Southern Resistance fighters had been killed.

The Saudi-led coalition began its campaign on March 26, striving to reverse months of advances by the Houthis after they moved from their northern stronghold last year, capturing the capital Sanaa and pushing south to Aden.

A senior Houthi commander, Abdul-Khaliq al-Houthi, was captured on Saturday by the Southern Resistance, the secessionist movement said on its official Twitter account.

Houthi officials could not immediately be contacted for comment. Reuters could not independently verify the information.

Yemenis say Abdul-Khaliq al-Houthi, a brother of Houthi leader Abdul-Malek al-Houthi, played an important role in the militia's capture of Sanaa in September.