Security officials say Yemen's Shiite rebels and government forces are shelling each other in areas south of Hodeida, straining an already shaky cease-fire in the Red Sea port city.
They said each side blamed the other for Saturday's shelling, and that both were reinforcing their forces in the city in violation of the U.N.-brokered truce reached in Sweden last month.
The violence coincided with the arrival Saturday in Sanaa of U.N. envoy Martin Griffiths, his first visit to Yemen since the Sweden talks.
The officials spoke on condition of anonymity because they were not authorized to brief the media.
Yemen plunged into civil war in 2014 when the rebels known as Houthis captured Sanaa. A Saudi-led coalition intervened in the war a year later, fighting alongside government troops.