Nearly a quarter of the population in drought-hit Djibouti is in desperate need of aid, with malnutrition and a dramatic lack of water causing a mass exodus from rural areas, the UN said on Thursday.

"Persistent and recurring droughts have resulted in a general lack of water for both people and livestock," said the UN's Djibouti coordinator Robert Watkins.

The crisis, which has dragged on since 2010, has left a full 190,000 of the country's 850,000 residents in need of humanitarian assistance.

They include 27,500 refugees, mainly from neighbouring Somalia, Watkins told reporters in Geneva.

Yet the crisis in Djibouti has received little international attention, with a UN appeal for aid last year reaching only a third of its target -- the lowest level of funding for any such appeal worldwide.

The appeal comes amid warnings from Britain on Thursday that Somalia's Al-Qaeda-linked Shebab insurgents were planning further attacks in the tiny and traditionally tranquil Horn of Africa country.

Shebab suicide bombers hit a crowded restaurant in Djibouti last month, killing at least one, in an attack apparently linked to the country's participation in the African Union force in Somalia.

Djibouti's port also serves as a key base for international anti-piracy operations off the Somali coast.

Watkins also said on Thursday that some 60,000 migrants -- most of them Ethiopians trying to reach the Gulf for work -- were also in need of aid inside Djibouti.

Last year alone, 100,000 passed through the country, he said. Most migrants come on foot, staggering alongside the roads in the extreme heat.

"Many die from dehydration," he said.

Foreigners are not the only ones on the move in the country, where most people still live off livestock which have been hard-hit by the drought.

"There has been a huge exodus of people living in rural areas," Watkins said, adding that the population in the capital Djibouti City had more than doubled since 2010, now home to 85 percent of the population.

Nationwide, a full 18 percent of the population is considered acutely malnourished, rising to 26 percent in some areas -- well above the 15-percent emergency threshold, Watkins said.

Sixty percent of the country's population was also suffering from diarrhoeal diseases, he said.

Watkins said he hoped the lack of interest from funders would change, pointing out that a new appeal last month for $74 million (55 million euros) was already 13 percent funded, with contributions from the United States, the EU and Japan among others.