Security officials say fighting is underway across Yemen on the third day of a humanitarian truce between a Saudi-led coalition and Shiite rebels.

The officials reported clashes Friday in the southern city of Aden, the western city of Taiz and the provinces of Marib and Shabwa. They spoke on condition of anonymity because they were not authorized to brief the press.

The fighting pits the Shiite rebels, known as Houthis, and allied military units against loyalists of President Abed Rabbo Mansour Hadi, who fled the country in March. A Saudi-led coalition has been targeting the rebels from the air.

The U.N. envoy to Yemen, Ismail Ould Cheikh Ahmed, has proposed peace talks in Geneva. Rebel spokesman Hamed al-Bokheiti says the Houthis are willing to hold talks in any "neutral" country.