A vessel carrying the first shipment of food aid in three weeks docked Sunday at the rebel-controlled Red Sea port of Saleef in western Yemen, a United Nations official said.
Abeer Etefa, a spokesperson for the World Food Programme for the Middle East and North Africa region, said some 25,000 tons of wheat will be offloaded early on Monday.
Saleef port is around 70 kilometres (45 miles) north of the key port of Hodeida, also on the Red Sea and in rebel hands.
Hodeida port is the main conduit for UN-supervised deliveries of food and medicine and vital to UN efforts as it is closest to the majority of people in need.
Earlier this month, a Saudi-led coalition battling Iran-backed Huthi rebels imposed a blockade on Yemeni ports and airports in response to a missile fired by the Huthis that was intercepted near Riyadh airport.
The UN humanitarian affairs office had said on Friday that it had been given clearance by the coalition that has been fighting the rebels since 2015 to resume flights into Sanaa.
But it added that desperately needed shipments of food and medicines to Hodeida remained blocked.
On Sunday, a ship did dock at Hodeida, but the WFP's Etefa said it did not belong to the UN aid agency, and that it might be a "commercial" vessel.
The deputy head of Hodeida port, Yahya Sharafeddine , confirmed to AFP over the phone that it was indeed a "commercial" ship not linked to WFP aid.
"The ship in Hodeida is for traders. The one in Saleef is for WFP," he said.
UN officials have warned that Yemen could face the world's largest famine in decades unless the crippling blockade by the coalition is lifted.
A UN plane carrying desperately needed vaccines landed in the rebel-held Yemeni capital Sanaa on Saturday after coalition forces partly lifted the blockade, after warnings that thousands of people could die.
The coalition intervened to prop up Yemen's government after the Iran-backed Huthis drove it from Sanaa.
The devastating war has since killed some 8,600 people, while a further 2,000 have died of cholera.
Yemen is highly dependent on imported wheat for its basic needs, and aid groups have warned that humanitarian deliveries cover only a small portion of what is required.
The UN says more than 11 million children in war-torn Yemen are in desperate need of humanitarian aid.