GENEVA/SANAA (Reuters) - Humanitarian aid workers and medical supplies began arriving in the Yemeni capital of Sanaa on Saturday, 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 Sanaa this morning with humanitarian aid workers,  the World Food Programme s regional spokeswoman Abeer Etefa told Reuters in an email, while officials at Sanaa airport said two other U.N. flights had arrived on Saturday. 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.  Sanaa airport was closed from Nov. 6 until today, more than 18 days and this closure caused an obstruction to the presence of aid workers,  he told Reuters in Sanaa.   There are more than 500 employees trapped either inside or outside being denied travel as well as 40 flights that were denied arrival at Sanaa airport.  Colonel Turki al-Maliki, spokesman for the Saudi-led military coalition that closed the ports, said three more aid flights had been approved for Sunday. The coalition, which is fighting the armed Houthi movement in Yemen with backing from the United States, said on Wednesday 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 on Saturday supplying weapons to the Houthis. Iranian foreign ministry spokesman Bahram Qasemi said that Tehran would welcome the lifting of blockade and  any initiative that alleviates the pain of Yemeni people.  Maliki said on Friday that 82 permits had been issued for international aid missions since Nov. 4, both for Sanaa airport and Hodeidah, the country s main port where some 80 percent of food supplies enter.   That includes issuing clearance for a ship today (Rena), carrying 5,500 metric tonnes of food supplies, to the port of Hodeidah,  he said. He told Reuters on Saturday that the commercial vessel had been checked and cleared by coalition navy forces and was approaching Hodeidah, but port officials said no ships had arrived yet and they were not expecting any to dock soon. Maliki said new procedures aimed at blocking weapons transfers stipulate that aid and commercial shipments cannot be mixed on the same vessel, that requests require 72 hours notice instead of 48, and that only humanitarian workers can travel on aid flights. The blockade has drawn wide international concern, including from the United States and the U.N. secretary-general. Sources in Washington said Secretary of State Rex Tillerson had asked Saudi Arabia to ease its blockade of Yemen before the kingdom decided to do so.  The heads of three U.N. agencies had earlier urged the coalition to lift the blockade, warning that  untold thousands  would die if it stayed in place. The coalition has asked the United Nations to send a team to discuss ways of bolstering its verification and inspection mechanism programme which was agreed in 2015 to allow commercial ships to enter Hodeidah. 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. 