“I am extremely concerned with this trend at a time when the country is in the midst of a difficult transition that may lead to increased humanitarian needs," UN Humanitarian Coordinator in Afghanistan, Mark Bowden, said in a statement.
The departure of Western troops will leave Afghan forces to fight the Taliban-led insurgency on its own, a security concern for foreign workers and their Afghan colleagues working on development and reconstruction projects across the nation.
Bowden's comments followed the execution of nine aid workers in two separate incidents in Afghanistan this month.
According to the Aid Worker Security Database, 73 humanitarian workers have been killed, kidnapped or injured in Afghanistan since the start of the year, more than recorded for the whole of 2012.
The figure is also the highest since the organisation began collecting the data in 1997.
In an attack on Nov. 26, three aid workers were blown up by a remote controlled bomb in southern Afghanistan.
In the second attack on Nov. 27, six aid workers with a French aid group in the west were shot by gunmen in an ambush.
A total of 36 aid workers have been killed in Afghanistan so far this year, the United Nations said.
It gave no comparative figures but said the trend highlighted the growing risk surrounding the delivery of aid.
In a deadliest year for aid workers since the Taliban were ousted in 2001, both civilian and security force casualties have also soared in Afghanistan this year.