"I am angered that the enemies of Afghanistan have killed a brother and fellow Muslim in pursuit of their goal of disrupting reconstruction in Afghanistan," Karzai said in a statement Wednesday.
The engineer, identified as Eyup Orel, was abducted Tuesday along with two Afghans, a driver and an interpreter, in Kunar province as they were driving to the city of Jalalabad. The engineer was in Afghanistan working on a road project.
He was apparently shot several times after security forces closed in on his captors, the BBC reported. His Afghan colleagues had been released earlier.
It is not clear who was behind the killing. Kunar province is seen as a base of support for Gulbuddin Hekmatyar, a hard-line former mujahedin leader who has called for Karzai's overthrow. Members of the Taliban and Hekmatyar's Hizb-i-Islami -- accused by the United States of sponsoring terrorism -- are thought to operate in the area.