Somalia has seen a surge in fighting, despite a ceasefire pact last month
Humanitarian agencies in Somalia are considering suspending operations after two aid workers were shot dead in less than 24 hours.
Some aid organisations are reported to be reviewing their security measures following the attacks.
Violence against aid workers in Somalia has increased dramatically in recent weeks. But it is not clear exactly who is behind the attacks.
Half of Somalia's population needs food aid due to drought and conflict.
Two men were shot in separate incidents on Friday about 13 kilometres from the capital, Mogadishu.
Mohamed Mohamud Qeyre was killed. He was the deputy director of a local aid group affiliated to the German organization "Bread for the World."
"Two men shot him three times in the head and the ribs," a witness said.
Another man who worked for an organisation linked to the United Nation's World Food Programme is said to be in a serious condition.
In a third incident, another aid worker was killed in Galharei town in central Somalia.
"He was going to a mosque and he stepped out of his home," said local clan elder Ahmed Shire Yabar. "Two men armed with pistols shot him four times and escaped. He died on the spot," he said.
Friday's shootings bring the total number of aid workers shot last week to five.
A senior Somali aid worker for the UN was kidnapped last month, and another shot dead a week ago.
A driver for the World Food Programme was killed at a checkpoint on Monday.
The BBC's Mohamed Olad Hassan in Mogadishu says it is not clear who is behind the killings, since many factions in Somalia's chaotic war stand to benefit from the violence.
Our correspondent says powerful local leaders have complained that aid workers are feeding Islamic insurgents who had sworn to fight the government, and insurgents have also targeted Somalis affiliated with foreign organisations in the past.
He says the problem has been compounded by the growth of professional kidnapping rings, who security experts say have been encouraged by the large cash ransoms paid by foreigners to release ships taken by pirates.