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(CNN) -- Two Americans were killed during an exchange of fire in northeastern Afghanistan on Saturday, Afghan and U.S. officials said.

An Afghan "shooter" was also killed in the incident, Afghanistan's intelligence agency said.

This comes on the same day that newly appointed Defense Secretary Leon Panetta arrived in Afghanistan for a visit with U.S. and Afghan officials.

A U.S. Embassy spokeswoman told CNN the two were U.S. Defense Department personnel assigned to Forward Operating Base Lion. They were killed and another Defense employee was wounded, she said, in an exchange of fire in Panjshir province's Darah district.

"This is the first exchange of fire incident since the Provincial Reconstruction Team was established in November 2005," assistant press attache Megan Ellis said in an e-mail.

One of the two was a civilian, according to NATO's International Security Assistance Force, which called the Panjshir incident an attack.

Authorities the shooting involved an argument that broke out when a NATO vehicle was stopped by the intelligence agency in Darah district, said Gen. Qassim Genghal Bogh, police chief of Panjshir province. He said the intelligence agency staff opened fire.

"We don't know what was the main reason of the argument," Bogh said.

The National Directorate of Security, Afghanistan's intelligence agency said the Americans were working for a provincial reconstruction team. The Afghan "shooter" who exchanged fire with the Americans also was killed, the agency said.

CNN's Eve Bower and Joe Sterling contributed to this report.