— The United Nations declared on Monday that famine had spread to a sixth region in southern Somalia, warning that at least 750,000 people were now at the risk of death if aid efforts are not stepped up.

The spread of the crisis arrives even as international aid organizations have launched a massive effort to funnel food and medicines into Somalia as well as refugee camps in neighboring countries since the United Nation declared a famine in July. But a mixture of civil war, crop failures, high food prices, and restriction on the delivery of aid by al-Shabab, the al-Qaeda-linked insurgent group, have now placed more than 4 million Somalis in crisis — more than half the entire population.

On Monday, the United Nations added the Bay region, where an estimated 58 percent of all children are acutely malnourished, to the list of famine zones. Hundreds are dying every day in southern Somalia, mostly children.

“We can’t underestimate the scale of the crisis,” said Mark Bowden, the United Nations’s top humanitarian official for Somalia.

The worsening famine is unfolding as Somali leaders are meeting in Mogadishu to endorse a “road map” to tackle important tasks over the next year that diplomats hope will pave the way for a functioning and stable government.