Aden and the other southern provinces of Yemen have been largely inaccessible to UN food aid, and around 13 million people - over half the population - are thought to be in a situation of "critical" or "emergency" food insecurity.
"It's the first WFP chartered ship to berth in the port since the conflict erupted in late March," spokesman Peter Smerdon said.
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"We have additional ships chartered which are on standby heading towards Aden carrying more food and fuel."
Last week WFP negotiated the entry of a convoy of food trucks into Aden province, but said docking a ship was impossible because of fighting raging around the port area.
Since then Yemenis and a Saudi-led coalition fighting against the country's dominant Houthi militia and its army allies have broken months of stalemate by seizing the airport and then driving the Houthis out of their last redoubt in the west of the city.
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Smerdon called on the warring sides to allow distribution of food aid from the ship and to allow resumption of commercial trade, which he said was the only way to meet Yemen's food needs.
"We (the UN) cannot fill that gap," he said. "That gap can only be filled by the commercial sector being allowed to import food and deliver throughout the country."
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