The war in Yemen is "back in full force," the United Nations mediator Martin Griffiths told the Security Council on Tuesday amid renewed attempts to get the warring parties to talk. 

He said new fronts in the war is opening up in Hajjah and Taiz and Hudaydah. "The war is back in full force," he told the 15-member council.

A Saudi Arabia-led military coalition intervened in Yemen in 2015 after the Iran-aligned Houthi group ousted the country's government. The Houthis say they are fighting a corrupt system.

The UN describes Yemen as the world's worst humanitarian crisis. Some 80% of Yemenis need help, with 400,000 children under the age of 5 severely malnourished.