UNITED NATIONS - UN Secretary-General Ban Ki-moon on Thursday called for an immediate halt to the fighting in Yemen, the first time he has made such an appeal since Saudi-led air strikes against Iranian-backed Houthi rebels began three weeks ago. 'I am calling for an immediate cease-fire in Yemen by all the parties,' Ban said in a speech to the National Press Club in Washington. 'The Saudis have assured me that they understand that there must be a political process. I call on all Yemenis to participate in good faith.'