"Two female journalists were shot this morning inside a district police headquarter, one has been killed, while the other is seriously wounded," Khost provincial spokesman Mobarez Mohammad Zadran told AFP.
Zadran and deputy Khost police chief Yaqub Mandozai said that the gunman was wearing police uniform. The woman is the second Western journalist killed in Afghanistan during the election campaign, after Swedish journalist Nils Horner was shot dead in Kabul on March 11.
AFP's senior Afghan reporter Sardar Ahmad, his wife and two of his three children were killed on March 20 when gunmen smuggled pistols into Kabul's high-security Serena hotel and shot dead nine people including four foreigners.
Horner, 51, a veteran of Swedish national radio, was killed while researching a story about a January attack on a nearby restaurant which killed 21 people, including 13 foreigners. Khost province borders Pakistan's restive North Waziristan tribal area, a stronghold of the Haqqani militant network blamed for numerous high-profile attacks in Afghanistan, many targeting foreigners.
Kabul has been rocked by a string of high-profile attacks in the run-up to tomorrow's election, which will be the first democratic handover of power in Afghanistan's turbulent history. In addition to Horner's murder and the Serena assault, a charity's guesthouse has come under attack, along with offices of the Independent Election Commission (IEC).
Most recently, six police officers were killed in a suicide bombing at the interior ministry in Kabul on Wednesday. Security was tight across Afghanistan, ahead of the vote to elect a successor to President Hamid Karzai, who is constitutionally barred from standing again.
More than 400,000 personnel including police, army and intelligence services have been deployed to ensure security around the country, Interior Minister Omar Daudzai said.