Kabul, Afghanistan (CNN) -- At least 21 Afghan policemen have been killed in attacks across the country since last week, as the nation struggles to ready its local forces in expectation of a NATO withdrawal.
Police said eight men were killed Thursday in a Taliban attack in the southwestern Afghan province of Farah. Two other policemen were reported missing and presumed captured, Farah police Chief Shams Rahman Zahid said.
On Monday, four policemen and two civilians died after they were poisoned in the restive southern province of Helmand. A firefight ensued, and several militants were killed, according to a provincial report.
Last Thursday, an Afghan policeman shot and killed nine other officers in Paktika, a volatile province in the country's southeast. Two policemen were arrested, and another, believed to be part of the attack, fled, authorities said.
The Taliban claimed responsibility for the attack, saying in a statement that the officer who fired the shots was actually a Taliban fighter.
The shooter was a member of the Afghan Local Police force, according to International Security Assistance Force spokesman Maj. Joe Buccino.
Buccino described the shooter as a "rogue" and said the attack was not preceded by any signs of trouble.
This year, 16 of 76 NATO service members killed in Afghanistan have died at the hands of Afghan security forces.
Gen. John Allen, the commanding general of U.S.-led forces in Afghanistan, said officials are working on a new procedure to check the background of Afghans who sign up to join the security services. Allen has also touted the growing capabilities of Afghan national forces, who are increasingly expected to take over the country's security and are widely considered a critical element of NATO's drawdown strategy.
America's so-called surge forces departed this summer, and policymakers continue to grapple with the details of an eventual U.S. withdrawal.
The latest killings come after a shooting rampage in Afghanistan last month left 17 villagers dead in the Panjwai district of southern Kandahar province.
A U.S. soldier, Staff Sgt. Robert Bales, has been charged with murder.