Ismail Ould Cheikh Ahmed told reporters after briefing the U.N. Security Council behind closed doors that all parties to the conflict are responsible for the dire suffering of the Yemeni people until there is "a true cease-fire."
The humanitarian crisis in the Arab world's poorest country has escalated as the conflict has intensified.
Ground fighting and Saudi-led airstrikes targeting Yemen's Shiite Houthi rebels killed nearly 100 people Wednesday.