Yemen's warring parties exchanged heavy weapons fire overnight in Hodeida, residents and military sources said, as the United Nations scrambled to salvage a cease-fire deal in the Yemeni port city that is a lifeline for millions at risk of starvation.

The clashes were the heaviest since the ceasefire went into effect on Dec. 18, residents said, and came as the United Nations announced a deal setting out details of a mutual military withdrawal envisaged by the Stockholm truce accord.

Iran-aligned Houthi forces traded artillery, mortar and rocket salvos with troops of a Western-backed, Saudi-led coalition late on Sunday and early on Monday, with explosions heard across the Red Sea city, residents said.