By Aziz El Yaakoubi RIYADH (Reuters) -United Nations and United States envoys on Wednesday welcomed unilateral truce moves by Yemen’s warring sides as encouraging steps, while stressing the need for a more comprehensive ceasefire that would help alleviate a dire humanitarian crisis. The Saudi-led coalition fighting Yemen’s Houthis had said it would temporarily halt military operations from Wednesday after the Iran-aligned group this week declared a three-day cessation of cross-border attacks and ground offensives in Yemen. As part of efforts to end the seven-year-old war that has killed tens o…