The ports of and Mukalla, controlled by the internationally recognised government, are two of the four main entry points for food and aid into the country. control the other two main ports.
More than six years of fighting between the government and the Iran-backed rebels, who control much of the north, has caused major damage to the Aden and Mukalla ports, raising war risk premiums and, by default, the price of food passing through.
Yemen imports 90 percent of food for its 30 million population, according to the United Nations Development Programme (UNDP).
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The UN agency said 60 percent of total food imports into the impoverished country last year came through the rebel-controlled Red Sea ports of Hodeida and Salif, followed by the ports of Aden (36 percent) and Mukalla (three percent).
Fixing the ports will "reduce the cost of food in Yemen," Auke Lootsma, the UNDP's resident country representative, told AFP.
"The looming famine in Yemen is a question of food affordability and not food availability."
"For example, 50 percent of a kilogramme price of wheat is made up of transport costs, such as shipping, insurance and demurrage."
The UNDP warned last month that famine could become part of Yemen's "reality" this year, after a donor conference sought to raise $3.85 billion from more than 100 governments and donors, but only reached $1.7 billion.
In its damage and capacity assessment report, the UNDP said that $49.6 million - $21.6 million for Aden and $28 million for Mukalla - was needed to maintain current port operations and restore those operations to pre-war conditions.
Doing so would help reduce war-risk premiums, the UNDP said.
"With Yemen on the brink of wide scale famine, the timing of the ports' restorations is more critical than ever," said the report.
"If port infrastructure such as buoys, navigations systems and cranes were fixed, costs to shipping companies would decrease, ultimately making food more affordable to Yemenis and more humanitarian aid available."
The UN describes Yemen as the world's worst humanitarian crisis.
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