High levels of malnutrition, combined with ongoing violence in the war-torn Horn of Africa nation, are threatening "a human tragedy of unimaginable proportions", the UNHCR warned.
Following several seasons of failed rains and spiralling global food prices, drought has hit more than 12 million people across Somalia, Ethiopia and Kenya.
Thousands of Somali refugees are making perilous journeys of hundreds of miles to seek assistance: 54,000 people crossed into Ethiopia and Kenya in June alone. Levels of serious malnutrition amongst newly arrived children in Ethiopia are exceeding 50 per cent, while in Kenya levels are reaching 30 to 40 per cent.
Aid agencies have warned of the grave threat of famine but many are desperately short of funds: Britain's leading 13 agencies have said that they face a shortfall of more than £85 million for their emergency response in the region. Many have launched fund-raising appeals – Oxfam is describing its £50 million appeal as its biggest ever for Africa.
Many refugees arriving in Kenya are streaming into Dadaab, the world's largest refugee camp and already overflowing before the latest crisis.
Reports suggest that young children are dying as families wait to be registered.
"People are making incredibly gruelling journeys: some are walking for more than 20 days without food or water, facing attacks from armed groups or wild animals," Andrew Wander, Emergency Media Manager for Save the Children, told The Daily Telegraph. "Children are most vulnerable upon arrival after the strain of the journey."
UNHCR has described the needs for food, shelter, health services and other life-saving aid as "urgent and massive". And government representatives in the region warned that the situation could deteriorate further.
"We haven't seen the worst of this drought yet," Mohamed Elmi, Minister for Development of Northern Kenya, told The Daily Telegraph. "In Kenya, which is already significantly affected by the drought in Somalia, malnutrition levels are well beyond emergency levels and saving lives is becoming our major focus."
Underscoring the severity of the crisis, Islamist militants in Somalia have lifted a two-year-long ban on foreign aid agencies.
Al-Shabaab, the al-Qaeda-linked insurgency that is fighting the western-backed Transitional Federal Government, said that foreign aid agencies would be allowed access to drought victims in al-Shabaab-controlled areas.
Since 2009, the ban has further complicated an already difficult humanitarian environment in Somalia, where few international agencies work on the ground.
Al-Shabaab had accused aid agencies of being anti-Islamic or hosting spies, but said that organisations wanting to "assist those suffering" would now be granted access.
The United Nations has welcomed the announcement with caution.
“Al-Shabaab’s announcement is genuinely welcome, if there is substance to it,” Mark Bowden, the United Nations Humanitarian Coordinator for Somalia, told The Daily Telegraph.
“These areas are facing a particularly acute situation, with some of the highest malnutrition rates in the region. They are also where much of the migration is coming from, so if we can address the problems in the Al-Shabaab-controlled areas, it will help Ethiopia and Kenya as well.”