The United Nations has condemned attacks on aid workers in northern Uganda as the charity Oxfam announced it was suspending its operations there.
Ugandan civilians live in constant fear of attacks
At least two workers were shot dead in three separate attacks on Tuesday and Wednesday by suspected members of the rebel Lord's Resistance Army (LRA).
In recent years the LRA has rarely targetted aid workers.
The ambushes follow arrest warrants issued by The International Criminal Court against the five top LRA leaders.
This move may have changed the LRA's tactics, the BBC's Will Ross in Kampala says.
The LRA is accused of widespread murder and torture during nearly 20 years of fighting against the army and have kidnapped thousands of children.
"It is unconscionable that the LRA is carrying out these vicious attacks on unarmed humanitarian worker," UN emergency relief co-ordinator Jan Egeland said in a statement.
"The people of northern Uganda are heavily dependent on humanitarian aid, and access to them is already precarious," he said
Oxfam say they have suspended their operations in Kitgum and Pader districts due to the "unprecedented" and serious nature of the attacks.
"We work with about a quarter of a million people in about 10 camps and we've had to suspend movements of staff and people who work with us in the field," Oxfam's Emma Naylor told the BBC's Focus on Africa programme.
She said that the army's focus on finding a military solution to the northern rebellion meant displaced people were often left without adequate protection from the army and local militia.
"What we're seeing in the last couple of days is a product of the government of Uganda's failure to protect its own citizens who're displaced in the north and the aid agencies who're trying to give them much needed relief," Ms Naylor said.
Some 1.5m people have been displaced by the conflict, which has gained notoriety for the LRA's massacres and its tactic of kidnapping children for use as soldiers and sex slaves.