GENEVA, Humanitarian aid workers and medical supplies has arrived in the Yemeni capital of Sana'a, U.N. officials said, after the easing of a nearly three-week military blockade that sparked an international outcry.

Aid groups have welcomed the decision to let aid in but said flights are not enough to avert humanitarian crisis. About 7 million people face famine in Yemen and their survival depends on international assistance.

"First plane landed in Sana'a Saturday morning with humanitarian aid workers," the World Food Programme's regional spokeswoman Abeer Etefa said, while officials at Sanaa airport said two other U.N. flights later arrived the same day.

The U.N. children's fund UNICEF said one flight carried "over 15 tonnes" of vaccines that will cover some 600,000 children against diphtheria, tetanus and other diseases.

"The needs are huge and there is much more to do for #YemenChildren," the world body said on Twitter.

Airport director Khaled al-Shayef said that apart from the vaccinations shipment, a flight carrying eight employees of the International Committee of the Red Cross had also landed.

"Sana'a airport was closed from Nov 6 until Nov 25, more than 18 days and this closure caused an obstruction to the presence of aid workers," he said.

"There are more than 500 employees trapped either inside or outside being denied travel as well as 40 flights that were denied arrival at Sana'a airport."

Colonel Turki al-Maliki, spokesman for the Saudi-led military coalition that closed the air and sea ports, said three more aid flights had been approved for Sunday Nov 26.

The coalition, which is fighting the armed Houthi movement in Yemen with backing from the United States, said it would allow aid in through the Red Sea ports of Hodeidah and Salif, as well as U.N. flights to Sanaa.

The coalition closed air, land and sea access in a move it said was to stop the flow of Iranian arms to the Houthis, who control much of northern Yemen.

The action came after Saudi Arabia intercepted a missile fired toward Riyadh. Iran denied again supplying weapons to the Houthis.

Maliki said on Nov 24 that 82 permits had been issued for international aid missions since Nov 4, both for Sana'a airport and Hodeidah, the country's main port where some 80 percent of food supplies enter.

The coalition joined the Yemen war in 2015 after the Houthis forced President Abd-Rabbu Mansour Hadi and his government to flee their temporary headquarters in the southern port city of Aden into exile in Saudi Arabia.

The conflict has killed more than 10,000 people and displaced over 2 million, triggered a cholera epidemic, and driven Yemen to the verge of famine.