An Afghan policeman shot two foreign journalists working for Associated Press in eastern Afghanistan today, killing one and critically wounding the other, the news agency said.
The attack took place on the eve of a presidential election that Taliban insurgents have pledged to disrupt through a campaign of bombings and assassinations.
The two journalists were in a remote small town on Afghanistan's border with Pakistan when the incident took place.
AP said photographer Anja Niedringhaus had been killed and reporter Kathy Gannon wounded while they were sitting in their car.
Ms Niedringhaus, 48, an internationally acclaimed German photographer, was killed instantly, according to an AP freelancer who witnessed the shooting.
Canadian reporter Ms Gannon, 60, was wounded twice and was described as being in stable condition and talking to medical personnel, AP said.
AP Executive Editor Kathleen Carroll, speaking in New York, said: "Anja and Kathy together have spent years in Afghanistan covering the conflict and the people there.
"Anja was a vibrant, dynamic journalist well-loved for her insightful photographs, her warm heart and joy for life. We are heartbroken at her loss.”
AP said Ms Niedringhaus and Ms Gannon were travelling in a convoy of election workers delivering ballots from the centre of Khost city to the outskirts, in Tani district.
The area borders Pakistan's lawless North Waziristan region where many al-Qaeda and Taliban-linked militants are based.
The two had arrived in a heavily guarded district compound shortly before the attack. As they were sitting in the car waiting for the convoy to move, a unit commander walked up to the car, yelled "Allahu Akbar" [God is Great], and opened fire on them with his AK-47, AP said.
He then surrendered to the other police and was arrested.
Last month, a prominent Afghan journalist with the Agence France-Presse news agency was killed alongside eight other people when Taliban gunmen opened fire inside a heavily fortified luxury hotel in the centre of the capital, Kabul.
Also in March, a gunman shot dead Swedish journalist Nils Horner, 51, outside a restaurant in Kabul.