Yemen needs $716 million in aid this year, or 22 percent more than 2012's requirements, UN agencies said on Tuesday, after improved security enabled a reassessment of the humanitarian situation.
"We are hoping that we will be able to raise the whole amount so that we can comprehensively meet the needs and save lives," said the head of the UN Office for the Coordination of Humanitarian Affairs in Yemen, Trond Jensen.
"The humanitarian situation in Yemen is urgent and people's lives are at stake," he said in Dubai, warning of high malnutrition rates.
Jensen said the United Nations hoped that through "traditional donors, Yemeni partners, and partners in the region we will be able to raise the entire amount".
Last year, $329 million was raised from the $585 million that was needed.
But this year, the increase in "stability in some areas -- the south and north... has enabled reassessments," said Jensen.
"We found there are more people food-insecure than we thought, and we also found that more people are in need of nutrition support than we previously thought.
"There have been positive developments but the humanitarian situation has not changed," he added.
Yemen was rocked in 2011 by an uprising that left the already impoverished country's economy in tatters and weakened the government's control over several areas, especially across the south and east.
The country is now undergoing a transition period led by President Abdrabuh Mansur Hadi.
But the UN Development Programme representative in Yemen, Ismail Ould Cheikh Ahmed, warned that the "humanitarian crisis, which is a huge and critical crisis, can jeapordise the entire political process if it was not addressed."
Thirteen million people from Yemen's 24 million population do not have access to safe water and sanitation, while 10.5 million are food-insecure, according to UN figures.
"We have today 300,000 children who are in risk of dying or having their lives impaired because of malnutrition," said Ahmed, warning that "this figure can go nine times higher if there is no proper nutrition assistance."
Nearly 50 percent of Yemen's population are children and almost one million children under the age of five suffer from acute malnutrition.
During the uprising that ousted former strongman Ali Abdullah Saleh, the southern province of Abyan was the site of fierce battles between Al-Qaeda-linked jihadists and troops which fought for a year over control of the region.
The battle, finally won by government forces last June, has led to the destruction of Abyan as residents fled to nearby cities, mainly Aden.
"The government has been able to regain the territory of Abyan province and we have been successful in returning at least 90 percent of the internally displaced persons back to Abyan," said Naveed Hussein of the UN High Commissioner for Refugees.
There are however still 431,000 internally displaced persons in Yemen who have fled from several other areas across the south and north, the scene of on-off battles between Shiite Zaidi rebels and Sunni Islamists.
But "the government needs to improve the rule of law," said Hussein, adding that "supporting returns in Abyan is the top humanitarian priority."
In addition to its own problems, Yemen is also faced by the burden of refugees and migrants pouring into the country from the restive Horn of Africa, mainly Somalia and Ethiopia.
"The numbers of people coming into Yemen continues to increase, most of them from Ethiopia," said Hussein.
In 2011, the UNHCR recorded 103,000 refugees, asylum seekers and migrants crossing the Gulf of Aden and Red Sea into Yemen -- almost double the 2010 figure of 53,000. A reported 130 of them drowned.
Their number has now reached 269,000 registered refugees and 100,000 vulnerable and stranded migrants.