Yemen's warring sides clashed south of the Red Sea port city of Hudaydah late on Saturday, after Houthi fighters moved into territory ceded by forces allied to a Saudi-led coalition, military sources and witnesses said, reported Reuters.
Yemeni forces backed by the United Arab Emirates had on Friday announced they were redeploying from around Yemen's main port in the west, a move which a UN monitoring mission and the government said they had no advance notice of.
The Saudi-backed government and the Iran-aligned Houthis, who hold Hudaydah city, had in 2018 agreed a United Nations-sponsored pact for a truce in Hudaydah that largely held and a troop withdrawal by both sides, stalled since 2019.
Coalition warplanes launched air strikes on the Al Faza area south of Hudaydahas Houthi fighters battled UAE-backed forces until midnight, two military sources and residents said.
Al Faza lies 15 km (9 miles) from coalition-held Al-Khokha, to which hundreds of Yemenis have fled after the Houthi advance.
A UN mission overseeing the Hudaydah pact, UNMHA, on Saturday urged both sides to ensure the safety of civilians, saying it "was not informed in advance of the movements".
The internationally recognised government's team for UNMHA said in a statement it also had no prior knowledge and warned that Houthi advances would be "a glaring violation" of the pact.
It was not clear if the withdrawal in Hudaydah was linked to what the Saudi-led alliance had described as a redeployment in south Yemen, where sources said the Saudi military had left a main base in Aden, the interim seat of government.
Saudi Arabia's foreign minister, in an interview with France 24 TV on Saturday, reiterated a coalition denial that the Saudi military was withdrawing, saying "there continues to be strong support for the government of Yemen and (coalition) forces".
The alliance intervened in Yemen in 2015 after the Houthis ousted the government from the capital, Sanaa. The conflict is seen as a proxy war between Saudi Arabia and Iran. The Houthis say they are fighting a corrupt system and foreign aggression.
Washington is pressing Riyadh to lift a coalition blockade on Houthi-held ports, a condition from the group for ceasefire talks.
Hudaydah is the main entry point for commercial goods and aid flows and a lifeline for millions facing starvation in what the UN describes as the world's biggest humanitarian crisis.