GENEVA (Reuters) - The United Nations appealed on Friday to the Saudi-led military coalition to fully lift its blockade of Yemen, saying up to eight million people were  right on the brink of famine . Earlier this week the coalition partially eased its blockade to let aid into the ports of Hodeidah and Salif and U.N. flights into Sanaa. But aid shipments cover only a fraction of Yemen s needs, since almost all food, fuel and medicine are imported. The coalition, which is backed by the United States and other countries, began the blockade on Nov. 6 after Saudi Arabia intercepted a missile fired from Yemen toward its capital Riyadh. A second missile was shot down on Thursday.  That blockade has been partially wound down but not fully wound down. It needs to be fully wound down if we are to avoid an atrocious humanitarian tragedy involving the loss of millions of lives, the like of which the world has not seen for many decades,  U.N. humanitarian chief Mark Lowcock said.  Yemen has a population of 25 million people. Twenty million of them need assistance and something like seven or eight million of them are, right now, right on the brink of famine,  he said as he launched the U.N. s 2018 humanitarian appeal. Lowcock sidestepped reporters  questions on whether the Saudi-led blockade amounted to a violation of international law, though he said the United Nations had consistently urged all parties in the conflict to respect their obligations.  I m not a lawyer but clearly international humanitarian law includes a requirement to facilitate unhindered access for aid agencies, and that s what I ve been trying to secure both in what I ve said publicly and also in my private dialogue,  he said. U.N. officials are often shy of criticizing parties to a conflict for fear of losing access or funding. Saudi Arabia has been a major donor to aid appeals for Yemen. Others have been less reticent. Jan Egeland, a former U.N. aid chief, has called the blockade  illegal collective punishment , while  Alfredo Zamudio, director of the Nansen Center for Peace and Dialogue in Norway, told Reuters he thought the International Criminal Court should investigate whether it was a war crime. Speaking at Friday s event in Geneva, Helle Thorning-Schmidt, head of Save the Children International, said:  What we ve seen in Yemen has been actually a very clear breach of the rules and also it s been very clear that denial of aid coming in has also become a weapon of war.  The coalition joined the Yemen war in 2015 after the Iran-allied Houthi group and its allies forced President Abd-Rabbu Mansour Hadi to flee into exile in Saudi Arabia. Riyadh sees the Houthis as a proxy for Iran, its arch-foe in the region. The conflict has killed more than 10,000 people and displaced over 2 million and triggered a cholera epidemic as well as pushed the country to the verge of famine.     