A UN plane carrying desperately needed vaccines landed in the rebel-held Yemeni capital Sanaa on Saturday after a three-week Saudi-led aid blockade that had sparked warnings thousands could die.

Three other aircraft -- two carrying UN aid workers and one carrying International Committee of the Red Crossstaff -- also landed at the airport, which was repaired earlier this week after a Saudi-led air strike knocked out its radio navigation systems, an AFP correspondent reported.

The UN humanitarian affairs office had said on Friday that it had been given clearance by the Saudi-led coalition that has been fighting the rebels since 2015 to resume flights into Sanaa.

But it added that desperately needed shipments of food and medicines to the rebel-held Red Sea port of Hodeida remained blocked.

An official from the rebel-run civil aviation authority confirmed that the flights had landed.

But he warned that Saturday's aid delivery was not enough and demanded access to Sanaa airport for all flights in order to "save the lives of the sick", the rebel-run Saba news agency reported.

In a statement to the rebel-run Al-Masira television channel, Huthi leader Abdelmalek al-Huthi urged his supporters to remain mobilised against any "new Saudi escalation".

The UN children's fund UNICEF said Saturday's flight was carrying more than 15 tonnes, or 1.9 million doses, of vaccine for diphtheria, tetanus and other preventable diseases.

The World Health Organization said earlier this week that diphtheria was spreading as children went unvaccinated and doctors in Hodeida reported three deaths.

More than 2,000 people have died of cholera in Yemen this year, adding to the 8,600 who have been killed in the conflict between the Saudi-backed government and the rebels since 2015.

The aid blockade, put in place after the rebels fired a missile which was intercepted over Riyadh airport, has tightened the stranglehold on Hodeida, the conduit for UN-supervised deliveries of food and medicine to rebel-held territory.

The UN humanitarian office said that a ship loaded with wheat and another with equipment to treat the cholera epidemic are ready to head to Hodeida as soon as the Saudi-led coalition gives the go-ahead.

The coalition had said it would lift its blockade of the port from Thursday but it remains in place.

The United Nations has warned that unless the blockade is lifted, Yemen will face "the largest famine the world has seen for decades".

Yemen is highly dependent on imported wheat for its basic needs, and aid groups have warned that humanitarian deliveries cover only a small portion of the need.

Seven million Yemenis are completely dependent on relief supplies for their survival, according to the UN.

Source: AFP