Famine spread to a sixth southern Somali region and will likely extend further in the coming four months, the United Nations said Monday.
"Acute malnutrition and the rate of crude mortality have surpassed famine thresholds in Bay region of southern Somalia," the UN Somalia Food Security Nutrition Analysis Unit (FSNAU) said in a statement.
"Assuming current levels of response continue, famine is expected to spread further over the coming four months," the statement added.
The Bay area, which includes the major town of Baidoa, is a stronghold of hardline Islamist Shebab insurgents who have imposed severe restrictions on aid into the areas they control.
"Tens of thousands of people have already died, over half of whom are children," the statement added.
Famine was first declared in the southern Bakool and Lower Shabelle regions of southern Somalia in July.
It later spread to three further areas, including into the Somali capital Mogadishu and the Afgoye corridor, the world's largest camp for displaced people.
Al Qaeda affiliated Shebab fighters pulled out of positions in Mogadishu last month, but still control much of southern Somalia, the worst-hit region by famine and the extreme drought.
Famine implies that at least 20 percent of households face extreme food shortages, acute malnutrition in over 30 percent of people, and two deaths per 10,000 people every day, according to UN definition.
Several areas are at severe risk of tipping over into famine conditions, it added.
"An additional 50,000 people in cropping areas of Gedo and Juba and pastoral areas of Bakool face famine-level food deficits," the statement read.
"In total, 4 million people are in crisis in Somalia, with 750,000 people at risk of death in the coming four months in the absence of adequate response."
Some 12.4 million people in the Horn of Africa, including parts of Ethiopia, Djibouti, Kenya and Uganda, are affected by the worst drought in decades in the region and are in need of humanitarian assistance, according to the UN.