Save the Children has called for the unconditional and immediate release of a British security consultant who was kidnapped in Somalia.
The consultant, and a local worker, who was later freed unharmed, were seized in Adado near the Ethiopian border.
A spokeswoman for the charity said: "The other man abducted at the same time - a British national who was born in Zimbabwe - remains captive."
She said the charity was extremely concerned for his welfare.
She added: "The two men were working with Save the Children whilst the agency carried out a feasibility assessment into setting up a programme to help sick and malnourished children and their families in the area."
She added the charity, which has been working in the country for more than 40 years, had not yet been contacted by the group behind the kidnapping.
The BBC's Mohamed Mwalimu had earlier said the kidnapping came amid fierce fighting involving tanks and heavy artillery around the town of Adado.
The security consultant had gone to the area to see if it was safe enough for Save the Children to set up a new base to help malnourished and sick children, along with their families.
But on Thursday evening, a group of masked gunmen stormed the building used as a staff residence.
High walls and a heavy steel gate reportedly forced the kidnappers to climb in through a window before they fled with their hostages into an area said to be controlled by the hardline Islamist group al-Shabab, which has links to al-Qaeda.
Adado is also closely linked to pirate groups who routinely take ships and crew hostage and demand hefty ransoms.
Until now, Adado had been seen as a relatively stable part of Somalia, with aid groups considering relocating there after being forced out of more volatile regions.
Several foreigners have been kidnapped in Somalia in recent years.
Most have been freed unhurt after a ransom has been paid.