Yemeni rebels hit back at government forces advancing up the Red Sea coast, killing a deputy army commander in a missile strike, a military source said on Wednesday.

Army deputy chief of staff Major General Ahmad Saif Al Yafii was killed by a heat-seeking missile on the outskirts of the coastal town of Mokha, the source told AFP.

Another 18 soldiers as well as 21 rebels were killed in the clashes between Iran-backed Huthi insurgents and a Saudi-led coalition supporting the Yemeni government.

More than 50 others from the two sides were wounded in the fighting, which saw the coalition carry out air strikes as the rebels reached the eastern outskirts of Mokha.

The army had overrun Mokha on February 10.

Tuesday's clashes were a major setback for an offensive launched by government forces in January to try to recapture Yemen's 450 kilometre (280 mile) Red Sea coastline, which had previously been almost entirely in rebel hands.

Government commanders had talked confidently of pushing north towards the rebel-held port city of Hodeida, a vital conduit for UN-supervised aid deliveries to rebel-held areas.

The loyalists' February capture of Mokha was their biggest success in months.

Despite nearly two years of military support from a Saudi-led coalition, government forces are still largely restricted to the south and areas along the Saudi border.

The rebels still hold the capital Sanaa and much of the central and northern highlands as well as the coast around Hodeida.

Before the 19th Century, Mokha was Yemen's main port and export hub for coffee grown in the highlands and its historical symbolism meant it was fiercely fought over.

Its role was overtaken by Hodeida and second city Aden, where the government is based.

In addition to the war with the Huthis, the government and its forces have come under repeated jihadist attack.

Al-Qaeda fighters on Tuesday seized three trucks transporting arms in the southern province of Abyan, according to military and tribal sources.

The trucks had been delivering weapons to a pro-government coalition post in Taiz, located around 100 kilometres (62 miles) east of Mokha, the sources said.

Al-Qaeda and the rival Islamic State group have taken advantage of nearly two years of fighting between the government and the Huthis to entrench their presence in Yemen's south.

The conflict in Yemen has shown no let-up despite UN warnings of looming famine.

The UN humanitarian coordinator for Yemen, Jamie McGoldrick, warned on Tuesday that seven million Yemenis were close to starvation.

More than 7,400 people have been killed since the Saudi-led coalition intervened in March 2015, including around 1,400 children, according to World Health Organization figures.

McGoldrick said the death toll was closer to 10,000.