"We are no longer talking about a humanitarian crisis or a humanitarian emergency," said Jens Oppermann, the country director of Action Against Hunger (Action Contre La Faim, ACF).

"We are seeing this as a humanitarian catastrophe," he told AFP.

Thousands of Somalis have fled in recent months to neighbouring Ethiopia and Kenya in search of food and water, with many dying along the way, as the region suffers what the UN has described as the worst drought in decades.

Many too have risked conflict by fleeing into Somalia's capital Mogadishu in a desperate search for aid.

Food prices in Somalia have soared by 270 percent in a year, he said.

"We see people coming into Mogadishu in a state that we have not seen in this form before," Oppermann added, describing "unimaginable suffering beyond the scale of what is acceptable."

"We are not able to provide enough assistance to everyone," he said.

ACF has been working in Somalia since 1992.

Meanwhile Doctors without Borders (MSF) said they were boosting efforts to support refugees fleeing across the border into Kenya after assessments found "alarmingly high rates of malnutrition."

"I expected to find a difficult situation but not a catastrophic one," said Anita Sackl, who coordinates nutritional assessments for MSF.

"The majority of new arrivals actually fled because they had nothing to eat, not just because their country has been at war for decades," she added.

Refugees are waiting for 40 days before being registered, receiving only two days of rations for that period, MSF said in a statement.

In Kenya's Dadaab refugee camp, 37.7 percent of children under five checked by MSF teams were suffering from acute malnutrition, with 17.5 per cent of those facing a "high risk of death."

Scanty or failed rainfall in the region over the past two years has already forced thousands of Somalis to flee the country and ruined the livelihoods of millions in parts of Kenya, Ethiopia and Djibouti.

"We are possibly seeing a perfect storm in the coming months.... We are going to do everything we can to ameliorate it," UNICEF director Anthony Lake told AFP on his way to the drought-hit region of Turkana in north Kenya.

"We are scaling up in every way we can.... It is very bad now. There will be no major harvests until some time next year. The next six months are going to be very tough," added Lake.

Turkana is one of Kenya's badly affected regions where malnutrition rates have increased to 37 percent, compared with 15 percent in 2010, according to the aid organisation Oxfam.

A nurse in Lodwar, Turkana's main town, said the number of children admitted suffering malnutrition had doubled since last year.

"It (the drought) is the worst I have ever seen. We have admitted twice the number of children compared to last year," said Anne Lojao.

"Many children arrive already malnourished and weak and some are irritable, but they are the lucky ones who make it here."

Kenya is also home to the world's biggest refugee camp, where hundreds of thousands of Somalis have sought refuge from relentless conflict back home and thousands more are arriving daily due to the current drought.

Relief groups are struggling to cope with the influx and have urged the Kenyan government to ease camp congestion by opening a new camp that has already been constructed.

The camps that are currently operational host 380,000 people, more than four times the initial capacity.

Western countries and other donors have pledged millions of dollars in aid for the drought-stricken population but Lake said more still needed to be done.

Britain promised 52 million pounds (59 million euro, 73 million dollars) in emergency aid, in a statement Saturday from International Development Secretary Andrew Mitchell.

"The situation is getting worse and is particularly devastating in Somalia, where families already have to cope with living in one of the most insecure countries in the world," Mitchell said.

He called for doing "more to help not only refugees but also those victims of the drought who remain in Somalia."

UNICEF said last week it needed 31.8 million dollars for the coming three months to assist millions of affected women and children.

The organisation estimates that more than two million children in the region are malnourished and need urgent help, while some 500,000 of them face imminent, life-threatening conditions.

Experts have called for long-term measures to deal with the effects of recurring drought, arguing that the resultant human suffering can be avoided.

"Although governments and their development partners cannot make the rains come, they can mitigate the impact of these recurring droughts in East Africa," Kevin Cleaver of the International Fund for Agricultural Development said this week.

He argued that governments and donors should invest more in agricultural research to develop drought resistant crops and fodder for livestock.

The regions in the Horn of Africa often affected by cyclical drought have also been neglected by governments, with no electricity, roads, water and other basic health and education facilities.

These arid regions, many of them far removed from capitals, have also seen frequent inter-clan clashes over scarce resources as well insurgencies.