UN humanitarian aid chief Stephen O'Brien warned today that the war-torn and impoverished country Yemen faces "serious risk of famine" unless international donors step up their response.<br/>'<br/>The under-secretary-general for humanitarian affairs, speaking in the southern city of Aden where he met President Abedrabbo Mansour Hadi, also urged both sides in Yemen's two-year-old war to grant humanitarian access to the conflict zones. <br/><br/>He said we now face a serious risk of famine if the international community doesn't step up with funding and respond and the parties in the conflict continue to restrict humanitarian access.<br/>'<br/>He told a news conference that 19 million of Yemen's 26-million population now needed humanitarian aid, and "seven million Yemenis don't know where their next meal is coming from.<br/>