Somalia's Al Shabab extremist rebels stormed and looted the offices of the World Health Organization and several aid agencies working in the country's famine zone, according to the BBC.
The aid agencies warn that the lives of more than 150,000 children are at risk by cutting off their deliveries of food aid.
The Islamist militants stormed aid offices in the towns of Baidoa and Beledweyne, which like many southern areas are controlled by Al Shabab, according tot he reports.
Al Shabab has restricted the work of international aid groups but on Monday the rebels banned 16 groups outright, accusing them of political bias.
The move will prevent thousands of critically hungry children from getting food, according to the aid agencies. Somalia's years of conflict mean that the country is the worst affected by East Africa's current drought. The lack of rain is said to be the worst in 60 years.
The list of groups banned outright included the United Nations children's agency, Unicef, and other UN bodies, the British charity Concern and groups from Denmark, France, Germany, Italy, Norway, and Sweden.
The Unicef office in Baidoa was occupied and closed by a group of men suspected to be Al Shabaab, said Unicef spokesman Jaya Murthy.
"They just said they [Unicef staff] should go home immediately and our office is now their office," said Murthy to the BBC's Focus on Africa program.
Unicef was involved only in humanitarian work and Al Shabaab's decision will threaten the lives of thousands of children, said Murthy.
"About 160,000 severely malnourished children are at imminent risk of death if assistance does not continue," he said.
Al Shabaab accused the groups of exaggerating the scale of Somalia's problems for political reasons and to raise money. It also alleges that the agencies are working with church groups to try to convert vulnerable Muslim children and to oppose Al Shabab's attempts to impose Sharia law.
Aid groups banned by Somalia's Al Shabaab:
UN agencies including UNHCR, Unicef and WHO
Norwegian Refugee Council (NRC)
Danish Refugee Council (DRC)
Italy's Cooperazione Internazionale (COOPI)
Swedish African Welfare Alliance (SAWA)
German Agency For Technical Cooperation (GTZ)
France's Action Contre la Faim (ACF)
Not banned:
ICRC (Red Cross and Crescent)
MSF (Doctors Without Borders)
COSV (Italy)
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