(Adds Reuters tributes, details, Karzai statement)
KHOST, Afghanistan, April 4 (Reuters) - A veteran Associated Press photographer who had covered wars around the world was shot dead and another reporter was wounded on Friday when an Afghan policeman opened fire on them in eastern Afghanistan, the news agency said.
The attack took place on the eve of a presidential election in Afghanistan that Taliban insurgents have pledged to disrupt through a campaign of bombings and assassinations.
The AP said photographer Anja Niedringhaus, 48, was killed and reporter Kathy Gannon, 60, wounded while they were sitting in the back of a car.
Niedringhaus, an acclaimed German photographer who had covered conflict zones including Kuwait, Iraq, Libya, Gaza and the West Bank, was killed instantly, according to an AP Television freelancer who witnessed the shooting.
Canadian reporter Kathy Gannon, who is based in Islamabad and has covered war and unrest in Afghanistan for 30 years, was shot twice and was receiving medical help, the AP said.
Gannon underwent surgery in the eastern city of Khost. The operation was described as successful and Gannon's condition was stable, the AP 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 Executive Editor Kathleen Carroll, speaking in New York, told the agency.
The two journalists were in a remote small town on Afghanistan's border with Pakistan when the attack took place.
Taliban attacks on security forces, civilians and Westerners have been on the rise since the start of the year ahead of the vote, when Afghans will elect a successor to President Hamid Karzai, barred by the constitution from running again.
The assault on the AP journalists came just weeks after an Afghan journalist with the Agence France-Presse news agency was killed alongside eight other people when Taliban gunmen opened fire inside a 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.
AP President Gary Pruitt described Niedringhaus in a memo to staff as "spirited, intrepid and fearless, with a raucous laugh that we will always remember".
"Anja is the 32nd AP staffer to give their life in pursuit of the news since AP was founded in 1846," he wrote.
"This is a profession of the brave and the passionate, those committed to the mission of bringing to the world information that is fair, accurate and important. Anja Niedringhaus met that definition in every way."
SHOT BY POLICE
The AP said Niedringhaus and 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. 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 with his AK-47, the AP said.
He then surrendered to the other police and was arrested.
Reuters colleagues also sent tributes.
"Anja was an inspiration to two generations of photographers," said Chris Helgren, Editor-in-Charge, North America Pictures Desk.
"She was one of the world's best, who could produce an amazing image on the tennis court or the battlefield. She was seemingly fearless but also a very loyal friend with great wit, whose presence could brighten a grim assignment."
Reuters photographer Goran Tomasevic described her as "a dear friend and one of the best photographers in the world".
Word of Niedringhaus's death interrupted a U.N. briefing in Geneva, where she was based. A former colleague proposed a minute of silence, and friends paid tearful tributes.
"She was supposed to be iron-clad, this just seems so incredibly wrong," said Jonathan Fowler, a correspondent at AFP who previously worked with Niedringhaus at the AP.
Claire Nullis, spokeswoman for the World Meteorological Office in Geneva and a former AP colleague of Niedringhaus, said she had been wounded before.
"She used to shrug it off and get on with life. She was very affected by the recent death of an AFP journalist who was shot with a couple of his children and his wife in Afghanistan," she told the briefing.
"She was just the ultimate professional. She was a very, very dear friend. We would go swimming in the lake in summer. We would go to Bains de Paquis sauna in the winter. I will miss her dearly as will AP and the whole photographic world.
"She was very modest. She had a string of awards and she was very modest about it." (Reporting by Ilyas Wahdat in Khost, additional reporting by Tom Miles in Geneva, Writing by Maria Golovnina; Editing by John Chalmers and Ron Popeski)