Somalia's militant Islamist group al-Shabab has lifted a ban on foreign aid agencies, as the region is hit by its worst drought in 60 years.
Al-Shabab imposed the ban in 2009, accusing them of being anti-Muslim.
It now says all charities, whether "Muslims or non-Muslims", can give emergency aid as long as they have "no hidden agenda".
The UN told the BBC it welcomed al-Shabab's announcement, but it would need security guarantees for its staff.
"I welcome all efforts to ensure the people of Somalia can access the assistance which they have a right to," the UN humanitarian co-ordinator for Somalia, Mark Bowden, told the BBC's Focus on Africa programme.
About a quarter of Somalis have been displaced by the drought, with many fleeing to neighbouring countries.
Embarrassed
An al-Shabab spokesman, Sheik Ali Mohamud Rage, said the group had formed a committee to deal with the drought and aid agencies would have to liaise with it.
"Whether they are Muslims or non-Muslims, [if] their intention is only to assist those suffering, they can contact the committee which will give them access to the drought-hit areas," Mr Rage said at a press conference in the capital, Mogadishu.
"Anyone with no hidden agenda will be assisted... and those who intend to harm our people will be prevented to do so," he said.
Analysts say the move may have been prompted by the embarrassment al-Shabab feels about the exodus of Somalis leaving areas they control in search of food.
An estimated 12 million people in the Horn of Africa have been hit by this year's drought.
Its effects have been compounded by the violence in Somalia, which has been racked by constant war for more than 20 years - its last functioning national government was toppled in 1991.
'Tax worries'
In north-east Kenya's Dadaab refugee camp, some 1,400 refugees from Somalia are arriving every day. Aid agencies fear numbers could rise to half a million.
UN officials say more than 50% of Somali children arriving in neighbouring Ethiopia are malnourished - with some of them dying on their way to or within a day of arrival at refugee camps.
Mr Bowden said al-Shabab's decision to lift the ban could stem the flow of refugees, and reduce deaths.
"When people decide to move they suffer even higher rates of mortality," he said.
"If we can stop that situation and give people the food security they need to stay in Somalia we are going save more lives."
He said that he hoped al-Shabab would not demand payment in the form of a tax from aid agencies to operate in territory under its control.
"In the past, they honoured commitments and provided security for the agencies working there," Mr Bowden said.
"I hope they recognise that humanitarian agencies are going in only to meet the needs of the population."
Al-Shabab rules over large swathes of south and central Somalia.
It is fighting for Islamic rule in Somalia, and warned aid agencies in 2009 not to work with the weak central government, which only controls parts of the capital.
