A journalist has died and another has been wounded in an attack by Afghan police officer, a day ahead of the country's presidential elections.

German photojournalist Anja Niedringhaus, 48 years old, was a contributor for the Associated Press Television in the last 12 years.

She was part of a team that won a Pulitzer Price for covering Iraqi affairs, but also made special reports from Pakistan and Afghanistan.

Kathy Grannon, 60, is the AP's correspondent for Pakistan and Afghanistan. She is receiving medial treatment after having been injured, but is reported to be stable.

German magazine Der Spiegel has however reported that she was "seriously wounded" in the attack.

Reports by Der Spiegel suggest that a police unit commander was behind the attack. After shouting "God is great", he opened fire on the journalists while they were waiting for a convoy escorting them to move inside a security compound in the Tanay distict of Khost province, near the border with Pakistan.

After shooting at the two women, the policeman, a long-time officer, surrendered to his colleagues. His motives are yet unclear.

Two attacks against journalists were carried out by the Taliban in March. AFP's Sardar Ahmad and eight other people were killed at a hotel in the capital Kabul, and British-Swedish journalist Nils Hormer was shot dead on March 11, also in the capital.

The run-up to the elections has been described as the bloodiest since the Talibans were toppled down in 2001.

Data by Reporters without Borders has also shown that at least 19 journalists have been killed in Afghanistan for this stretch of time.

Security has been beefed up ahead of Friday's vote, which, in the words of a BBC correspondent, "is being protected by the biggest military operation since the fall of the Taliban", with nearly 200 000 troops deployed across the country.

The eight presidential candidates include former Foreign Ministers Abdullah Abdullah and former Finance Minister Ashraf Ghani Ahmadzai.

Acting President Hamid Karzai, who has held the office since 2001, cannot run for a third term due to constitutional restrictions.